He wrote the $130,000 check and received three smaller payments back from Trump. He can speak to all of that.
I'm no lawyer but I imagine the line of questioning will go something like this:
Prosecution: What is the reason that you wrote Stormy Daniels a check for $130,000?
Cohen: To ensure that she remained silent about her tryst with DT.
Prosecution: Was DT involved in this hush money plan?
Cohen: Yes. We met and discussed it several times.
Prosecution: Can you please speak to the reason that this $130,000 payment was necessary?
Cohen: DT, his team and myself all wanted to prevent this story from coming to light because we realized it could have significant impact the 2016 election.
Prosecution: In what way?
Cohen: DT did not want voters to know that he had an affair with a porn star. He knew it would likely cost him votes.
Prosecution: Why did you write the check?
Cohen: To avoid it being traced back to DT.
Prosecution: Who paid you back and how?
Cohen: I was reimbursed by DT, in three separate checks.
Prosecution: Mr. Cohen. Was this a cover-up?
Cohen: Yes. It was!