Which organ serves as the primary site of amino acid metabolism (i. e. oxidation, transamination, deamination, gluconeogenesis, etc.) ?

The liver

Explanation:

The liver -

In human beings the location of liver is just in the upper right portion of the abdomen, exactly below the diaphragm.

Liver is present in specifically vertebrates, and is responsible for various metabolism, like producing hormones, decomposition of the red blood cells, regulating the storage of glycogen and the synthesis of proteins.

Liver is the main site for the process of gluconeogenesis, amino acid catabolism.

Liver is the very organ, that has full urea cycle.

Hence, from the given information of the question,

The correct term is the liver.