I honestly have no idea.
Surface stuff confuses the hell out of me.
Yes I'm probably an stupid idiot.
I've shot stuff and got done for it where I thought I didn't before, and so now generally don't bother due to C+P punishing me for stuff I don't understand.
This probably means I am bad at planning or am not responsible enough.
Not really the players' fault IMO. If it's a bug, it should have been fixed by now, and since there was nothing in the patch notes to indicate that they were removing surface objects info, it's likely a bug. If it was intentional, then it's a very poor design decision - "Let's make it more difficult by not giving players the information they need to make a decision". Meh.
Anyway, to the potential workarounds, depending what you are trying to do on the surface, there's a decent chance of knowing skimmers and turrets status, and if we get it wrong, then at least the bounties that we get for our troubles are small (even destroying a skimmer or turret only counts as assault, not murder), and since you have no notoriety can be paid off immediately.
So, if the skimmers / turrets are guarding a non procedural (named) base they will very likely be clean so you will get bounties (with the exception being anarchy system / faction ones).
In my experience, if you are taking a mission to scan a planetary data beacon that is procedural (you will be sent to an unnamed outpost or building), then the defenses are always wanted, even if the target has a trespass zone. You will still get a bounty for scanning the data beacon if it's private, that's unavoidable, but you can shoot the skimmers or turrets if you want, and you'll even get paid if you destroy the skimmers...
If you are hunting skimmers or just casually salvaging stuff and find it by hunting random POI's, then the method I mentioned above works. Before you start shooting anything, target a canister. It (for reasons unknown) will still have info displayed, and that info will be 'Legal or Illegal Salvage' or sometimes 'Illegal in Jurisdiction'. If it's Legal Salvage, skimmers guarding will be wanted, if Illegal Salvage they will be clean. If it's Illegal in Jurisdiction that just means the contents is illegal, but typically the skimmers are wanted.