Endless Mike
Sqirrel Girl fanboy
Superman doesn't need to learn new powers, instead he needs to learn to undo his built - in mental blocks and release the powers he's already had.
One of the main reasons that Superman is stronger than Goku is that Goku always has to power up to fight his enemies, while Superman has to hold back to avoid doing too much damage.
In fact, it's been stated that there were only three times in his life when he truly went all - out:
1. When he was a little kid and couldn't use his powers yet and hit someone.
2. In the final deathblow against Doomsday when he killed him.
3. Against Imperiex in Our Worlds at War, where after sundipping, he managed to push War World (which was a battleship the size of Pluto) back across the solar system against its full - throttle countermeasure firing to stop him which was powered by energy gleaned from Imperiex (who had the power of the Big Bang as well as countless galaxies he had devoured).