Is there only client staking possible or are there also masternodes? If so, how much coins are needed for a masternode? If not, what is the daily return for staking?
Blackcoin maybe needn't something like masternodes. It's running on Proof of Stake static reward.
what does that mean exactely? for example: i hold 1000 coins in the blackcoin wallet. how much reward will i get a day?
does it have to be online all the time or is it like claming gas in NEO ?
It does have to be online all the time. You get around 6% compound interest per year at the moment, inflation is only 1% per year though.