Can we get POS reward when we just leave a wallet open with coins and not run a masternode?
Yes
Note that there is a minimum of seven days between the time you move the coins to your wallet and you receiving a stake.
Once coins have received a stake another seven day wait applies.
You can split your coins into multiple inputs to increase the potential to stake.
Do you need to go to setting and open your wallet + leave the program/wallet itself open in order to recieve a potential stake?