The Allen Center ("CSE" or, less formally, "CSE1") is the original CSE building (the one connected to ECE with sliding doors on the front). Most office hours happen in the 'breakouts' the breakouts are large open spaces adjacent to the staircases (look for the area with a big whiteboard and seating).
The Gates Center ("CSE2") is the new building. We often have office hours in CSE2 121 and 131 (located inside the undergraduate commons on the first floor) and in some of the smaller TA spaces on the first floor (just outside the commons)
Robbie's office is also in Gates -- take the elevator up to the third floor, turn left when leaving the elevators and you'll walk right into Robbie's office (room number CSE2 311).
Links for zoom hours can be found on Ed on the pinned post of important links.