Is 5h 50min enough of a layover to enjoy FCT and see rashi?
From Frankfurt Airport (FRA) to city center takes about 11 minutes by IC train (intercity), and 22 minutes by S-Bahn (urban rail).
If you want to go to Worms, to see the Rashi Synogogue (11th century, but rebuilt in 1961) - it would be about about an hour and
10 minutes by train. By car it's about 45 minutes if there no traffic. If you are flying on to a non-Schengen country, e.g. the US,
ensure that you arrive back at the airport about 90 minutes prior, as you have to go through passport control, and a couple of security
clearances.
Also, note, Rashi was buried in Troyes, France, albeit the exact location in the cemetery is unknown. Troyes is about 500km away from Frankfurt.