What exactly is the wavelength of a photon? Is it photons or E.M waves that are emitted from atoms? Do photons travel like a wave?

Photons are unusual things that have zero rest mass. As with other particles, they have the properties of a particle and the properties of a wave at the same time. You can use formula that explain the behavior of either and those formulas apply to photons. Their masslessness makes it much more apparent at a macro level than other particles. The wavelength of a photon varies with how energetic it is. There is no single wavelength, photons occur on all of the frequencies. This photon (when you choose to describe it as you would a wave) propagates like a wave, doing wave-like things, like diffraction or wave interference. Or you can describe it like a particle, shooting off in a line with a very high speed, emitted by atoms when the atoms change energy state. (Or do you want to describe that emitted energy as a wave, because you can.) So, in short answers to your questions: What exactly is the wavelength of a light? Any. Is it photons or E.M waves that are emitted from atoms? You can describe it either way and the formulas work. Does light travel like a wave? Yes, light travels like waves AND like particles. One problem here is you have some of the language a little confused. It is LIGHT that is describes as either EM Waves or as Photons. We normally use the term "photon" to indicate we are discussing light-as-a-particle. We use "EM Waves" or EM radiation to indicate we are discussing light-as-a-wave. Perhaps that will help you understand why the two are normally considered separately.

Light has a dual nature. If you ask me is light a wave or particle I would say it is neither. I claim this because when you say sound is a wave or a billiard ball is particle you can describe both of the situations with the same particular set of equations for all of space and time. But there is no such single set of equations. When light travels it is best described by Maxwell's equations and when it interacts with matter it can be described by quantum mechanics. So basically light travels as a wave interacts like a particle. And to answer how can you associate wavelength to a photon I would say that the photon has some energy which can be said is proportional to the inverse of wavelength. So with a particular energy of photon you can assign a given wavelength. Thus from all the above things I mentioned it can be deduced that photons are emiited from atoms and then they travel as electromagnetic waves.