Hi Fab
Most Märklin recent locos and cars have an NEM 361 pocket. This is a standard European interface for couplers and many other model train producers use them.
So in theory you may slide any standard coupler into those pockets
Märklin provides "Relex" couplings Ref is 72060 and chances are they are compatible with these former "Buckle" couplings as older Märklin cars and locos
Cheers
Jean

Hi Fab
I have no Piko loco but I know Märklin since the 60s.
From what I see your Piko loco is fitted with traditional Märklin coupling (the one used by Märklin from 1938 and 1988 and in this case with a solenoid-operated collapsing hook.
So all recent Märklin cars / Wagons made of plastic have 2 types:
- one with elongation mechanism and an NEM pocket --> replacement to old-style coupling is 72060 (an assortment of 10 couplings)
- the others with a fixed coupling vertical axle --> replacement to old-style coupling is 7205 (an assortment of 10 couplings for locos and 40 for cars)

Note: the KK coupling you show seems to have been modified

Here is a KK coupling (all identical but this one for old-style Märklin locos)

There is a little nose (circled in violett here) that you may bend a little to raise the buckle (one or 2 mm). Sometimes it helps getting a nice coupling with old-style Märklin couplers
After all the Marklin KK was designed to be compatible with the previous Märklin couplings (called Relex)

Relex coupling: here is one with a fitting for NEM 361 pockets

Cheers
Jean

Yes