Where is the string that generates the hash with 18-20 zeroes? When bitcoin miners mine, they have to solve a difficult and extremely repetitive math problem using the SHA256 algorithm. The miners are trying (basically playing lottery and almost always working in large groups) to get a hash with (currently) at least ~18.81 zeroes. (I put a decimal/float number because the value is inconsistent.) But, I want to put the hash into a hash function and get that super hard-to-compute number for a story I have where a superhero calculates this number. How do I get this string (nonce) that calculates to this zeroed hash and where do I find this on a block explorer, such as blockchain.com, or on bitcoin-cli?
If I undestend the your question,

This is an example of the proof-of-work algorithm.

The nonce is a component of the block, the strucure of the block contain the value, inside the blockchain.com you can find the value inside the propiety "nonce"

I hope I answered your question