Translation:I listen, except for when he speaks.
This is probably also due to the tense (see my post above). If you wrote "except when he is talking", the tense is incorrect. Talking translates as tá...ag labhairt, talks would be labhraíonn.
I think the issue is the tense. Speaking translates as tá...ag labhairt, speaks would be labhraíonn.
as of this module, verbal nouns haven't been introduced The suffix -a/i'onn is distinctly present habitual