This is simple due to the theorem of the mass-center motion: resultant force F acting on a landung jumper is equal to the product m*acm. As for F it is the sum of N+mg+Faero. As for the second this depends on whole body motion when landidg, Shoud be advised to make acm as small as it possible to prolong the time of the velocity decay: by moving hands down and bowing legs etc but not standing vertically as a colomn.
One of my papers might have what you are looking for "Bilateral contact ground reaction forces and contact times during plyometric drop jumping". It also addresses the forces in each leg.
Drop jump or running long jump? There are a lot of investigations about ground reaction force in drop jump, but there is normalised force usually. Probably participants of significantly varying mass will have significant differences in techniques of landing (and ground reaction force). It is difficult to measure ground reaction force in running long jump landing (Using CM-motion as orientir? It is possible only theoretically here. :)). And for what?