Tá ceist faoi cheisteanna agam.

What is the normal way to ask a question of the form "How do you [do something]?" in Irish, e.g. "How do you eat oysters".

Right away I would think of "Conas a itheann tú oisrí?"

But is it that simple? I suspect what that means is "How is it that you (presently) eat oysters?", which I might want to ask if I am surprised to find you eating oysters. I want to know how to ask, "How does one [do something]?", in colloquial Irish.

I think you can say "Caidé mar a ghníthear XYZ?" (Donegal), "Conas a dhéantar XYZ?" (standard Irish), etc.
Using the "briathar saor".

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

And in this special case:
Conas a itear oisrí?

And you can use the verbal noun:
Conas oisrí a ithe? (How to eat oysters?)

Go raibh míle maith agat, a Lughaidh agus a Labhráis!