If the school has a blazer / jumper as part of the uniform ask if the kids have free will to remove them. Some schools insist on blazers / jumpers on at all times, some schools the kids have to ask permission to remove them. My DD's secondary jumpers are optional. Blazers can be removed in the classroom but must be worn in the corridor.
That wasn't the only reason we chose the school but it was important to me that DD could manage her own comfort re: temperature.
Also ask about their transition plan from primary to secondary. My DD had visits at primary from some of the secondary teachers. Then she had 2 transition days in July. In Sept the Yr7s had 2 days in school with just Yr11s too. So had a chance to get their bearings without the full school being in.
Accessibility to toilets is a good question to ask.
Ask what pastoral support is available to the kids and how that is accessed.
Their disciplinary structure and how / when it is administered is a good one to ask about. At DD's school it's called a consequence: a C1 (consequence 1) is a warning. C2 is a 10 minute break time detention etc etc up to a C5.
Not that I'm saying that you need to know because of your DC but it's handy to know if your DC is in a class with someone who is disruptive, and how you can expect that to be dealt with.
After school clubs, what do they have on offer and are there any costs?
Breakfast club and any costs if you think your DC may access it.
Do they do homework clubs?
Examples of what is available for lunches. We got a copy of the current menu at the visits.