getbestblockhash RPC returns the header hash of the most recent block on the best block chain.
Result—hash of the tip from the best block chain
|The hash of the block header from the most recent block on the best block chain, encoded as hex in RPC byte order|
pai-cli -testnet getbestblockhash
GetBlock: gets a block with a particular header hash from the local block database either as a JSON object or as a serialized block.
GetBlockHash: returns the header hash of a block at the given height in the local best block chain.