Michael - donegal's a big place, but I'll be at Oideas gael in a tiny place called Glencolumbkille (Gleann Colum Cille) on the coast. There are sessions in any of the 3 pubs trhere - if not in one, try the othes! they are Biddy's, Roarty's and the Glen Head Tavern (this last usually not good, but local fiddler James Byrne and family often play there). Sessions seldom start much before 10pm.

Just over the hill is Carrick, where the Slieve Lague Hotel (it's a bar though) often have sessions, or go to Teelin to the Cúl an Dúin (might be renamed now - I hear new owners have taken over from the Altan crowd).

Further north I'm familiar with Hudi Beag's at Gweedore and also the Clannadh family pub on the way to Donegal airport, but I can't recall the name.
Hope you have a great time!
Slán - Dáithí