What framework can be used for answering product design questions in job interview ? e.g. How to design a microwave, pencil, bottle ?

I'd recommend the CIRCLES Methodâ„¢ for product design interview questions. 's visual above summarizes it, and I explain CIRCLES in more detail here:

If I ask a question around designing a product I expect the candidate to follow a structure such as the following: 1) Ask Clarifying Questions Remember, there is no point continuing with an answer if you haven’t fully grasped the situation. I can’t count the number of times I’ve asked a simple product improvement question to a candidate who then proceeded to give me a lengthy 5 minute answer before I realized that the candidate had never used the product before. If I asked a candidate to walk me through how he/she might design a better wallet, I expect the candidate to first ask clarifying questions such as who the wallet might be used by, or what “better” means in the context of a wallet. Remember, product managers don’t just dive headfirst into launching a product without first understanding the whole situation and the business goals. A candidate who doesn’t ask clarifying questions is a big red flag and tells me that he/she would design products without understanding what a user truly needs. 2) Communicate Your Answer Outline There is nothing worse for an interviewer than trying to follow a candidate’s unstructured train of thought when responding to a product question. It’s crucial to demonstrate that you have taken time to comprehend the situation and then lay out some groundwork as to how you plan to answer this question. Showing that you are organized and use structure when answering these questions will put your interviewer at ease and keep your thoughts in line so that you don’t ramble or go off on tangents. An example of how you might approach this is to say “Now that I’ve understood the scope of this product, I’d like to lay out how I might approach this design question. First, I’m going to re-iterate what my business goals are. Second, I’ll identify my customer base and their use cases. Third, I’m going to brainstorm some features and evaluate these features against the business goals I’ve listed. Lastly, I’ll discuss trade-offs and summarize my recommendation.” 3) Identify the Users / Customers and their Use Cases Although you might have lightly touched upon this while asking some clarifying questions, this step is crucial to locking down exactly who the product’s customers and users are and their use cases.  Remember that for certain products, a customer may not necessarily be using the product. For example, the educational app/games market often has parents as the customers who are buying these apps for their children to use. If it helps, I would recommend drawing a 2 column table on a whiteboard or piece of paper with your users/customers on the left column, and their respective use cases on the right column (users/customers may each have multiple use cases so leave some room on the right side to account for that). For example, going back to the better wallet, a user might be a working adult who uses a wallet to store their cash and critical cards (i.e. license, debit/credit cards/business cards). At this point, it would be great to ask more clarification questions to your interviewer about whether or not they want to focus on a particular user/customer to save time. 4) Identify Gaps in the Use Cases Now that you’ve compiled a list of various use cases, it’s time to start thinking about how current products/solutions in the market address these use cases and whether or not there are any gaps or room for improvement. Taking a step back, it’s good to look down your left column of users/customers and think about the qualities that are special to each one of them. Like a true product manager / customer advocate, put yourself in their shoes and think about their limitations and values. This will help you to better identify weak spots in current product offerings. If you want, you can add a third column next to each use case to help structure the obvious gaps that you locate. 5) Brainstorm Features / Improvements So now that you’ve figured out the potential gaps that current products are missing to address user/customer needs, it’s time to break out that thinking cap and brainstorm solutions to address these gaps. Make sure that your features / improvements match the use cases that you’ve listed and don’t be afraid to ask your interviewer if you are on the right track or if they prefer you to focus on one or two of your ideas. 6) Prioritize and Identify Trade-offs With this new shiny list of features and improvements that you’ve come up with, it’s time to prioritize which of these you might focus on and what the trade-offs would be with each solution. When you prioritize your ideas, it’s important to use some sort of structure. If you are focusing on business goals like revenue, it might be important to use prioritization framework such as considering revenue generated, time / cost to develop. One simple way is to take the (potential revenue generated – cost to develop ) / time to develop and first prioritizing your list this way. Otherwise, you can also prioritize off other variables like customer satisfaction depending on what your goals are. Once you’ve come up with this list, think about the pros/cons and trade-offs of choosing to implement each solution. This lets you automatically play devil’s advocate to your own ideas to show your interviewer that you are thinking about all facets of the solution including edge cases and potential negatives. As an interviewer, I love to see candidates critically think about their own ideas and tell me the trade-offs vs. requiring me to grill them. 7) Summarize your Recommendation Let your interviewer know what your final choice is and feel free to review how you came to the solution and why it satisfies a user/customer’s needs. If you haven’t elaborated enough already, feel free to reiterate why you chose this solution over the others on your brainstormed list. http://www.productmanagerhq.com/2014/07/product-manager-interview-the-product-design-question/

Thanks for the A2A. The previous answerers have provided lucid answers on frameworks. I'll just touch upon one step in the framework. You could use any of the three frameworks provided here to explain about product design. However to stand out, explain slightly more in detail about any modifications you will be planning to introduce in an already established design. For example, say you are given a pen to design, you could come up with a rubber pen. The utility of this rubber pen is especially for drummers. They can continue with their habit without disturbing people around them. Coming up with such ideas on the fly tells the interviewers that you are creative and that will skew the outcome in your favour.