They can check everything. Or they may not check it at all.
Speically your resident days (physical presence), exit and entry dates, any criminal offences. Also if you had any misreprentation (like if you lied about any information when you obtained your PR).
I don't think they go all the way back to how many hours you worked when you had your study permit... But well, if you've been trueful, there's nothing to worry about.