In this paper, we investigate the physical layer security (PLS) for reconfigurable intelligent surface (RIS)-assisted non-orthogonal multiple access (NOMA) system over generalized fading channels. Specifically, we assume that the system is based on RIS access point (AP) and RIS is used to improve the secrecy performance of two legitimate users. We adopt the FisherSnedecor F model to characterize the composite fading and shadowing channel. In particular, novel expressions for the outage probability and secrecy outage probability (SOP) are derived. We verify our analytical results through Monte-Carlo simulations. The results indicate that the secrecy performance is affected by the number of RIS reflecting elements and Fisher-Snedecor F composite fading parameters.