It doesn’t matter if you don’t know the answer; they’ll be interested to see how you formulate your answer and how you would go about finding out new information.
Is cuma mura bhfuil an freagra ar eolas agat; beidh suim acu san fhreagra a thabharfaidh tú agus sa bhealach a rachfaidh tú sa tóir ar eolas nua.