Which trace mineral is important for activating a key enzyme in gluconeogenesis?

The correct answer is Manganese (Mn).

Manganese functions as a cofactor for a large variety of enzymes with many functions including those active in gluconeogenesis. Pyruvate carboxylase that catalyzes breakdown of pyruvate to oxaloacetate requires manganese (or magnesium) for its function. Phosphoenolpyruvate carboxykinase also needs Mn.