We don't know.

I assume nothing, he is just an uber Elder God.

Perhaps Elder Gods in general don't control any element or don't have any specific function.

Or Shinnok may have lost his divine abilities when he fell out of grace.

Q

Raiden and Fujin aren't Elder Gods (okay, well, Raiden was till MKDA) they're elemental gods, meaning they control elements. Shinnok, however, was an elder god, not an elemental. Look at it like Greek mythology; you have Zeus and Hera, who are king and queen of the gods, therefore the head honchos. Then you have Hades, god of netherworld; Ares, god of war; basically gods of everything. Likewise, in MK mythology there are several elder gods, who created everything and have authority over other gods; and each realm has several elemental gods.

Which just got me thinking: why have we seen only Earthrealm elemental gods? Why not Outworld, or Edenia?

Shinnok was an Ex Elder God. But he is no longer a God. Even with the Amulet he's not as powerful as he used to be when he was a God.

There are only about 4 or 3 elder Gods in total. They rule all reality. And the elemental Gods are servanst of the Elder Gods on Earth realms