Does this store sell that Korean yogurt soda Milkis? (밀키스) also boba tea in a can?

That I do not know but more likely they do.

Not sure about the boba in a can. But they do have a little coffee shop inside that sells boba teas, smoothies and pastries

Next time I go , I'll see.

Yes

Milkis yes

I saw some but it was not a lot. It seems that is a popular item.

There selection may be limited on occasions but the have it.