Columbia doesn't have a secondary, the primary app is it! 😀
Tufts: like Boston U and Mayo, the secondary is basically just an excuse to ask you for more money, except for Tufts makes you type your name and AMCAS ID no. several times, who your LOR writers will be, why you're applying to Tufts (1/4 page), plus they want a picture.
JHU: (about 12 lines, < 2 inches allotted space per question)
Describe briefly how you selected your undergraduate school and major area of study.
Briefly describe your most rewarding experience or some achievement of which you are particularly proud.
Are there any areas of medicine that are of particular interest to you? If so, please comment:
Plus some questions about honors, activities, what you've done since graduation & plans for the upcoming year if you've already earned your bachelor's degree, and explain what you did if you interrupted your college education for a semester or longer.
I have no idea if they change these questions from year to year. Just do a search for the other schools (there were some threads devoted to this exact question this summer) if you must know this early, but, hey, what's the rush?