If you are talking about the FAFSA, which believe most colleges require you to complete, it has instructions/guidelines as to whose/what information is required....I know that I had to report mine and my DH's income (DH is DD's stepfather) because DD lives with us and we claim her as a dependent on our taxes. The form has a place for "pertinent information"...where I added that my divorce decree requres my ex to cover 1/2 of DD's post-secondary education costs.
Some colleges require their own forms/supplements as well as the FAFSA, the one we had to fill out is called the CSS Profile that a lot of private colleges require. The Profile asked me to provide my ex's name and address, and one of the colleges requested that a "non-custodial parent's information" supplemental form be submitted, because that particular college takes into account the non-custodial parent's assetts as well, I presume.
Each college has it's own policies for for determining your "need"

but they pretty much rely on the FAFSA information for dispensing federal aid and then the supplemental stuff can factor in awarding $$ available directly from the college.
As previous posters said, the colleges financial aid office should be able to help you....and although the FAFSA and other forms are intimidating, they have step by step instructions and there is also on-line help too, as you go through question by question.
It's a real pain.....good luck!!