How can I show leadership skills in technical job interviews?

Honestly, most fuzzy criteria like "leadership skills" are unlikely to be consciously evaluated by any of your engineering interviewers, and if you make a concerted effort to show them, it will likely seem prerehearsed and trite. Aside from acing your technical questions (on which you should be expending ~95% of effort), it would be more useful to see how you could fit in with the company culture (by talking about what developments interest you, your quirks, etc.). Also, be sure to exude passion for tech in general, and specifically for the company you're interviewing with - this can be done by doing some research beforehand, asking questions, making insights about their products, or a multitude of other options. Good luck on the job hunt!