"His legs are long."
Translation:Seine Beine sind lang.
Only for those of poultry ("Hähnchenschenkel") :)
We say "Oberschenkel" and "Unterschenkel" for the upper and lower leg, but not "Schenkel" for the whole leg.
A "Schenkelklopfer" is a knee-/thigh-slapper, a very effective (often crude) joke (often used ironically). I'd imagine "Schenkel" to mean "thigh" here.
Sometimes "Schenkel" ("leg", among other translations) is used in a technical context (for parts of tools or whatever); it also means one side of an angle.
I think it can't be Schenkel here because Schenkel is only leg in math and engineering or for some animals (as already said by stepintime), so it would be "its", not "his". Otherwise, you would be talking about the chicken legs of some butcher, for example, which is a bit far-fetched.