Eske byen konprann mwen oubyen mal konprann mwen...kisa fraz sa vle di? Is it asking if you understand fully or not fully?

Yes (for byen konprann)

Eske ou byen konprann mwen is asking do you fully / completely understand me.
but mal konprann translates to misunderstand
example:
Mwen byen konprann sa ou te di a.
I fully understand what you said.

Eske ou byen konprann kouman pou pran remèd la?
Do you fully understand how to take the medication?

Ou te mal konprann mesaj la.
You misunderstood the message.

Ou te mal konprann mwen.
You misunderstood me.
Haitian Creole ↔ English Reference, Look up Haitian Creole and English Words