I don't understand if each full node has different mempool inside.
With RPC command
getblocktemplate I can Get the information about candidate block.
I can Find all transaction verified but unconfirmed
And I can find even
target, the value for mining.
My mempool is different from another node? I have to Update my mempool before build candidate block ?
The mempool of all nodes is different, but this isn't an issue. There will always be some inconsistency due to latency, network conditions, and differing configurations. This doesn't measurably impact your income and won't effect the validity of blocks you produce.