Even if Goku becomes the strongest in his universe he wouldn’t be able to defeat an Omniscient being no matter what.
And if that being is Vegeta then there is absolutely zero chance of him winning since Vegeta will have the experience of his fights all over the years and the training he has gone through but most importantly his heart and will.
If Vegeta Was Omniscient, Could Goku Beat Him?
Goku would have to become an omniscient being himself to stand a chance against Omniscient Vegeta.
Otherwise, it will be the same as an average human being fighting a trained Saiyan, which will result in a one-sided massacre.