What to do after Staff level is all 20?

What do I do, what do I train?

Do you mean Designers / Marketers / Engineers / Mechanics?

If so you choose whichever bonus is more useful, +1% driver health, 10% reduction is cost of parts, 10% bonus to sponspors etc

but I already have them at level 20, before Q1 patch if u trained a level 20 skill it said: "nothing happens"

You still get the added secondary bonuses, as David has pointed out above.

Thanks