There is a small church in the center of SJPP, directly on the narrow street that pilgrims take to leave town. I know I've seen masses going on there, plus choral rehearsals and performances. The Pilgrim's Office at 39 Rue de Citadelle likely will know the times of the mass.
There is a daily mass in Roncesvalles. If you attend the last mass of the day, you will receive the pilgrim blessing, which is a fantastic Camino tradition. Here are the timings for the Roncesvalles masses:
Sundays and holidays
8'30h.; 12'00h.; 18'00h.; (from November to June)
19'00h.; (from June to October)
Saturdays and holidays eve
18'00h. (from November to June)
19'00h. (from July to October)
Working days (from Monday to Friday)
20'00h. (During the whole year)
The Pilgrim's blessing is given at the end of the last mass of the day, during the year, as long as the pilgrim ask for it.
The confessions are heard half an hour before the mass.
(From this website:
http://www.roncesvalles.es)