“What was it that you wanted me to look at?”
Your roommate wanted you to look at something on YouTube, but you were in the middle of writing something important so you wanted to finish it. Now you're finished writing it, and you want to know what your roommate was trying to show you.
What was it that you wanted me to look at?
When someone tells you something or asks a question, but you weren't able to pay close attention to it because you were busy or distracted, you can ask this question.
There are a few versions of this question:
What was it that you were saying?
What was it that you were asking?
What was it that you wanted to talk to me about?
Notice that the phrase always ends with a verb that's continuous and past (were saying, were asking, wanted).