Hi,
I have bought Cardano and put it in a Yorio-wallet. This was after the 29th of november. Is it still possible to stake? And how do I do this?
You cant. Need to wait for main net…
Staking is only live on testnet. The current testnet balances are based on the 29th november status. So you’ll have to wait for either a 2nd snapshot ( Still under debate if a 2nd one will occur) or wait till you can stake on mainnet once it’s released to mainnet.
If you use Daedalus, it will show a list of pools you can delegate to. Also the new Yoroi has a search option for pools. (And probably more options by the time you will be able to stake 
)
It looks like this in Daedalus:
There are several good websites to find a decent stakepool.