Terminal 1 at Frankfurt is broken into multiple different "concourses" - A, B, C and Z. Each of these concourse contains one or more Lufthansa lounges. In general, the best lounge to use is dictated by the location of the gate your flight is departing from. It is possible to access the other lounges in other concourses, although in many cases this will require passing through immigration and/or security - and generally there isn't any point as most of the lounges offer very similar services.
As Star Alliance Gold you have access to both the the Lufthansa Business Lounges and the Lufthansa Senator Lounges - the latter being slightly better, but only slightly. In most cases the two lounges are paired together (with a single entrance), although there are a few exceptions.
Specifically for Turkish flights, these generally leave from the B concourse. The nearest lounge would be the "Lufthansa B East" lounges which are above gates B44-48, and which contains both a Business and Senator lounge. Additionally there is also a Business lounge on the west end of the terminal, but this is not as good as the East one.