Does anyone know how to travel back to the states using a travel document?

My friend is trying to go back to the states with me. The problem is, he has nothing but a travel document. Is there anything he can do?

Can you travel from germany to other European countries wih a US Refugee travel document?

I am planning a Eurotrip this xmas and wondering if I can use my Refugee Travel Document to travel from one European country to another. Thanks!