Oh how i hate the ink stains on jeans, and I have had my fair share of it. I have used 2 different methods that have both worked well for me. You can put some paper towels in between the fabric so the ink doesn't absorb onto the the other half of the jeans. Using rubbing alcohol, pour it on the stain and let it sit for a minute and then blot it with another paper towel to bring out the ink. I have also used hairspray and applied on both sides of the ink stain. Same as with alcohol, blot it and keep repeating until the stain is gone.
Getting ink out of jeans is relatively simple. All you'll need is a can of hairspray. Spray the ink stain with hairspray and blot with a white washcloth. Try not to over saturate the area. Repeat as needed until the stain is gone. Wait until the jeans dry and then wash as usual.