She started to have trouble sleeping.What does sleeping modify in this sentence,is it "trouble" or the whole sentence?

Answer 1

Sleeping answers the question: what did she start to have trouble doing?

Since it was sleeping that she had started to have trouble doing, sleeping modifies trouble (it tells us precisely what the trouble was with).

I hope that was helpful and let me know if you have other questions!

Answer 2

It can be caused by stress