"What sport do you like the most?"
Technically, 你最喜欢做什么运动 is "what sport do you like TO PLAY the most," which is actually different.
Because (1) you already have 什么 as a question word in the sentence, and because (2) 吗 is only for questions that can be answered with 'yes' or 'no', which is not the case here.
Thw use of " She ma" Indicates that the sentence is a question, so ma isnt necessary.
什么 (shénme, what/which) is the question particle, so there shouldn't also be 吗
Because it requires an answer with "yes" or "no". In this case, the answer is a name of a sport.
Seems to me that "what's your favorite sport" would fit better, but maybe that's just me.