I know that this is fairly old but perhaps this will help someone. Not sure if the poster was trying to determine an EXISTING string or one to use to connect to another recordsource. If you want to connect to something other than the current project, you can find the connection string you want by going to http://www.connectionstrings.com
and it is a good reference.
If you want the existing connection string that would be something completely different and you can find it by holding your mouse over a linked table and the control tip text will come up and show how it is connected.