Who is responsible for debt of a second mortgage, when my ex granted me no liablility in our divorce agreement.

If your divorce agreement required her to be fully responsible for a second mortgage that had your name on it, but then filed for bankruptcy, he/she is required to indemnify you as a result of any judgment.  You may need to bring a motion in order to enforce the terms of the divorce agreement.    Please contact me if you would like to have a further discussion.