It's probably impossible to fully enumerate the characteristics of good questions. For the most part, we rely on people's judgment to determine which questions are good.
That being said, I think there are some heuristics. In my mind, they mostly depend on the idea of a "hypothetical student" who has studied physics up to the topic and level of the question. For example, given a question about general relativity, the hypothetical student is someone who would already be very familiar with Newtonian and Hamiltonian mechanics, electromagnetism, and at least some quantum mechanics, as well as prerequisite math topics like differential equations and linear algebra - perhaps an upper-level undergraduate or beginning grad student. On the other hand, for a simple question about heat transfer involving common objects, the hypothetical student could be a motivated layperson with some mathematical aptitude and the ability to search the web and identify useful sources. (Granted, this is not the most precisely defined concept, but it's a work in progress.)
I expect the asker of a question to have or find resources and education roughly equivalent to what this "hypothetical student" would have access to, and to use those resources and education to make an honest attempt to figure out the answer to the question themselves. As long as I'm satisfied that the asker didn't miss anything that the hypothetical student would have tried, then I'll probably consider it at least a decent question.
Note that I'm not saying the question body necessarily has to include the research/effort that was done. It's possible for a question to be good without describing what the asker checked beforehand. But if I, say, copy and paste the title into Google, I'd better not find that the top result is an answer.
Aside from that, if it looks like the goal of a question is to gain an unfair advantage in any way (e.g. cheating on a homework assignment or exam where outside assistance is not allowed), then I'll definitely consider it a bad question. Same goes for cases where the question appears to come from an educational setting but the asker isn't interesting in actually learning whatever it is they're supposed to be learning. (That being the idea behind our homework policy.)
Also, if a question is something that the "hypothetical student" would consider particularly insightful, i.e. something that students at that level typically wouldn't think to ask, then it's more likely to be a good question.