I am a co-signer on my sons trucking business. It is LLC. How am I obligated here? I am retired with personal investments. Are they protected should.

It depends what you signed.  A loan.  The LLC filing.  You do not say.

What do you mean that you are a co-signer?  Do you mean that you, individually, have co-signed for loans made to the business?  If so, you are responsible for paying those loans, and if they are defaulted upon, your assets, including personal investments, could theoretically be used to satisfy the debt.  If you only mean that you are a member of the llc, or can co-sign on its accounts, you would in most cases have no personal liability for the llc's obligations.