"Do you know a good school?"
Translation:Te ismersz egy jó iskolát?
I believe it's similar to German kennen/wissen, French connaître/savoir, Italian cognoscere/sapere, Spanish conocer/saber -- ismer is "be acquainted with" (a person or place) while tud is "know" (a fact). (And tud is also used for "know how to (do something), be able to (do something)".)
Yes, it is rather needed. The questions sounds like you are asking for advice, so don't care if I know good schools in general which would be suggested by this form:
- Ismersz jó iskolákat?
This one suggest there I doubt that there is any good school in the world, do you agree:
- Ismersz jó iskolát?
No. I want to go to school, and I am wondering if you can suggest me one, so I am asking:
- Ismersz/Tudsz egy jó iskolát?