In two-way full-duplex relay systems based on non-orthogonal multiple access (NOMA) for Beyond the Fifth Generation (B5G) networks, we propose a power control mechanism using successive convex approximation (SCA) to coordinate co-channel interference and improve spectral efficiency, which efficiently obtains suboptimal solutions for the original non-convex problem within polynomial time. To satisfy the low-latency requirements of B5G mobile networks, we further design a deep neural network (DNN) -based online power control mechanism. Simulations verify the effectiveness of both mechanisms, showing that the DNN-based approach achieves comparable performance to the SCA-based method while significantly reducing online computational time.