I am still a little bit confused about that staking...

How often should i open my wallet for best profit:
1. Once / week
2. Once / day
3. Keep it open 24 / 7
4. Other
Thanks in advance.
You won't need to open your wallet, it will stake as long as your address has balance in the network.
dev,
I think you are wrong , I didn't get any stake when my wallet is closed.
guys,
How about you?seems i have to keep it open 24/7 if i want to earn the stake.
no, you don't need. you still don't understand how the minting works.
thank you so much ekoja and ReRunRod and hashcash.
yes, I don't understand how the minting works indeed. I am a newbie to POS.
But my situation is like this : every day i sync my wallet first , if i close the wallet once synced , i got nothing through checking the transactions . if I kept it open , I got stake .
I don't understand why .

You cannot get stake with a closed wallet. That is wrong. Staking is like mining, it needs time to find blocks. The wallet should be left open as long as possible.
Every 'chunk' of coins that come into the wallet are elegible to mine stake after 1 day... but they are competing against the rest of the network. The larger and older they are, the more weight they have.