Which chakras best for channeling?

Questions : which chakra must be open and properly functioning in order to allow a being to speak through me (using my mouth) but not full possession?

throat chakra ? Zeal chakra?

Yes, I believe it’s a case of clairaudience where one speaks what is “heard” (telepathically, or sometimes almost physically) so throat chakra would indeed be involved.

You want all of them open and working orderly. If one is out of balance it can throw the others out as well.