I was using Ninki as my wallet, however, the service got discontinued

Yikes, sorry mate.

I cant access it how would I go to recover my bitcoin or is it completely lost?

Well, it depends. If you have a backup of the wallet, or a mnemoic seed phrase, you might be good to get your Bitcoins back. If Ninki does not let you do this, or you do not have one of these, your screwed.

You are not the only person facing this. Many wallets and exchanges close, taking their customers Bitcoins with them.