Many kinds of ink such as ball point pen ink, permanent markers, etc will dissolve in ethanol or isopropyl alcohol (rubbing alcohol). Test first in an inconspicuous area. If it works, use a little then be prepared to blot up the solvated ink quickly with dry cloth or paper towels and repeat. The alcohol will be very drying to leather (if that is what you have) so don't leave it for more than a couple of minutes at most, and treat the leather with some kind of conditioner afterward.