Tying a shoelace while wearing skinny jeans is really not very different from tying a shoelace while wearing any other kind of jeans. There are a few minor factors that you might need to take into consideration, but for the most part, it is a simple task.
Roll the pant leg of the jeans up a little so that you have a clear view of the shoe laces. You may try actually rolling the jeans, but you could also just pull them up so they are bunched a little near the calf. Preferably do this while sitting down so that you do not have to worry about the pant leg falling back down while you are tying the shoe.
Tie one shoe at a time keeping the pant leg pulled up so that it does not fall and interrupt your tying. Tie the two strings of one lace into an "X" formation, one going under the other. Then pull the two tight.
Swing one of the strings around to form one half of a bow. Clench one part of the lace in your hand and then fold another part of the string to form what looks like a bunny ear. Do the same thing with the other shoe lace.
Swing one of these ears below the other and back up and around. Pull them tight to form something of a bow. This will form your tied shoe lace. Once you are done, simply lower the pant leg and repeat these steps on the next shoe.