What is the recommended memory_target and memory_max_target for ORACLE 12 DB running on a dedicated server with 32GB RAM?
Forget memory_target and memory_max_target. AMM has always been a feature that worked on paper, but failed in practice. Oracle finally admitted it semi-officially as of the release of 12.2:



When I have no information about earlier memory usage, I just go with a 1:4 ratio for PGA:SGA target.

sga_target=20G
pga_aggregate_target=5G


Which implicitly sets:

sga_max_size=20G
pga_aggregate_limit=10G


Then later you can tune if needed, after observing the workload and memory usage.