If you think he was destitute and would have had to rely on Poor Law assistance in Ireland, you could check the workhouse records. There were 10 Poor Law Unions which covered Donegal. The inmate records for the 9 exclusively in Donegal are likely to be in the National Archives in Dublin, and the 10th – Londonderry (which included part of Donegal) will be in PRONI, Belfast.
Falkryn is right about the movement to and fro. There was an overnight ferry from Londonderry to Glasgow 3 times a week right up until the 1960s. Folk from Donegal went back and forth on this all the time. And being a domestic ferry service there are no passenger records for that type of journey.