What information can the feds see when they subpoena your iCloud data?

What information can they see like will it be text messages or just call records and text records of you texted?

They can see anything and everything.

I don't use iClud for anything, so they will see a blank.

It will be EVERYTHING on that device.

Assuming they are given access to the data, they can see EVERYTHING in the account.

They can see EVERYTHING. Yes, there's such a thing as computer forensics.