Ddr4 16GB RAM, 1x 16GB module
Ddr4 16GB RAM, 1x 16GB module
Does he already have another stick of 1x16GB? If not, order two sticks of 8GB at 3200Mhz CL16 or higher. Pick those specifications (or 3600Mhz CL16/CL18) and select the most affordable option from a trusted manufacturer (I usually go for G.Skill on AMD systems).
Considering 2x8GB RAM isn't ideal. For gaming, the distinction between single and dual-channel memory matters significantly.