(Japanese) Domo komo?

I’ve heard this used but not sure about the spelling- sounds sort of like domo kono/domo komo I think it’s slang

In what context have you heard it? If it’s ‘doumo, kono…’ it would mean ‘thanks, this…’ and would need a few words after it.
There’s ‘doumo, koumo nai’ which means literally ‘not any way or this way’, basically ‘there’s no way’.

It’s standard Japanese.

Apparently ‘doumokoumo’ is also the name of a fabulous two headed beast, but I don’t think that’s the word you were thinking of.