Wasting of calculated hashes If I am trying to find a nonce and in the meantime someone finds a nonce and adds a new block to chain, then will my work be wasted or it could be useful in finding other nonces?
your work is "wasted" caused by the mining-algorithm.

you have found a new block if sha2(sha2(blockheaderOfnewBlock) starts with a certain amount of zeros. the blockheader contains a nonce, the hash of the previous block and some other information. since the previous-block-hash is another hash if a new block was found you have another information-base for your mining-software.