Assuming you mean the J&J model (you didn't specify a year):
Length overall: 12.14m (that's the length from the frontmost bit of the boat to the rearmost bit, including whatever sticks out, davits, anchor, etc.) - this also varies if you stick a different anchor on
Hull length: 11.93m (that's the length of the fibreglass hull only, without any fittings)
Now depending on where you register the boat, different sizes matter. Under the German Flaggenzertifikat, the hull length is what's asked for, which is why these German built boats are often just shy of 12m hull length and the LOA is largely irrelevant
The registration office typically wants to see the builders data sheet with that number on it.
Under the UK SSR, the LOA is asked for, but no proof is needed, so experienced boat owners often will make small measurement mistakes when registering
They also commonly measure the boat without the anchor in place and davits are habitually forgotten or happened to be removed for maintenance.
For marina fees this only matters in some places, as many do not have strict 10-12-14m brackets. Some have 11-13-15m instead, others include the beam as well, in Spain they simply charge per square meter (length x beam). One place where it does make a big difference is if you're planning to go to Greece, where the price difference for the cruising fee is 30 EUR vs 100 EUR when going over the 12m mark.
So basically, don't let a few cm's on a bit of paper put you off buying a boat you like. And when it comes to registering, consider the above.