Of course there is a Yoda Cave on Iceland, why wouldn't there be one? If you're coming from the direction of Vik, follow the 1 Road for about 12km until you see a rock formation on your righthand side (looking south). There will be a small blue sign saying "Hjörleifshöfði", this is where you need to take a turn onto the gravel road. Just follow this road for about 2.5km and it'll lead you straight to the cave.
It's a bit small on the inside and there isn't much else to see around the area so this doesn't need to be an hour long stop, but rather a quick visit to snap that one photo you need!