Do any CryptoNote coins support merged mining?
If so which coins can be merged mined about how would merge mining affect my hashrate?
The Monero community almost unanimously voted against merged mining choosing instead to stand on its own and avoid indirectly supporting another CryptoNote coin, BCN that was 80% premined..
Actually voting is closed now as soon as nearly nobody wants merge mining in BMR
In hindsight measured by network hashrate, the Monero community made a wise decision. No other CryptoNote coin has close to the hashrate of Monero today.
FantomCoin can be merged mined with Bytecoin's/QuazarCoin's with no hit to network has rate. Its creation appears to have been inspired by the Monero rejection of merged mining:
FCN thread comment: "I think there was no need of another fork just for MM"
TFT: "Community around BitMonero was completely against MM this time and we could not include it in BMR. Amphibian decided to deploy his work this way. MM at least doesn't consume additional energy"
Townforge, a new fork of Monero which embeds a multiplayer game, can be merge mined with Monero (https://townforge.net/faq/#faq-13). The monero daemon must currently be patched with https://github.com/monero-project/monero/pull/6810 for the method from How can one merge mine Townforge with Monero? to apply though.
Your hash rate should not be significantly affected by merge mining: two more processes are running (townforged and a merge mining proxy) but they are not mining themselves so mostly leave the CPU alone. They can also run on a different machine if this becomes an issue.