There are innumerable ways to retrieve information about Bitcoin blocks, including previous block hash. If you're not running your own full node software, you can utilize some external blockchain explorer API to fulfill your needs. Of course, you may also need some additional software to massage the data you get from APIs because not all of them have advanced filtering to extract only the required data. For example, here is a simple script in Python for extracting block hash from specific block height:
thanks for the answer.
my question is, the nonce in header is the start nonce for mining I assume, right? where can I find exact nonce used to solve the target requirement for that block?
also when miner increment nonce, it should be placed in header and header hash recalculatet, right?
no, that should be the actual nonce... If you would re-create the header using this info and do a sha256d hash of said header, the outcome should be under the current target... Starting nonces are not included into the block header when it gets broadcasted.