undefinedhow do you stop your chain from jumping when its in 8th

Tie it down?

When does it jump? What front chain ring do you use when the chain jump?
Do you mean jump off? Then adjust the deraileur.
Do you mean ghost shift? Adjust cable tension.
Do you mean jump up and down when you jump on the bike? Just the deraileur spring working.
Do you mean jump "ahead"? Change chain or cassette.

By jumping i mean, when i shift to eighth it will stay in 8th but it will skip/jump when you put enough torque on it, this happens regardless what front chainring its on.

Get new chain and cassette

You may indeed need a new chain. I'm very cheap, so try this. Before you go that route, remove the chain and soak it in a pan of mineral spirits or kerosene for a while. Brush out any stubborn junk. Inspect for stiff links. Reinstall the chain and relube it with an oil type chain lubricant, not one of the wax types.

Doc