It is not glottal, it is velar. Both "h" and "ch" make that sound: https://upload.wikimedia.org/wikipedia/commons/0/0f/Voiceless_velar_fricative.ogg
Polish has two types of "know" and they are not interchangeable at all. I came up with the following explanation:
znać = to know X
wiedzieć = to know, that X; to know about X, etc.
For example: "Nie znam ich" (I do not know them), "Nic o nich nie wiem" (I do not know anything about them.
"Znam jego kota" (I know his cat), "Wiem, że jego kot jest gruby (I know, that his cat is fat)
"Znam odpowiedź" (I know the answer), "Wiem, jaka jest odpowiedź (I know what the answer is).
I think in a way you could understand "znać" as "to be familiar with".