Sit-ups do not help much in chin-ups. Your abs are supporting
muscles in chin-ups, but they're precisely that: they only play a
supporting role. You should be training your friend in assisted
chin-ups and strength training instead.
Jogging is a good form of cardiovascular exercise, but twice a week
is not enough if he's planning to lose weight and build up his
stamina. I would say that jogging on alternate days is better.
Heck, I go jogging three times a week.
And also, what kind of diet is he on at the moment?
