BIP-32 - how can parent extended public key exposed parent extended private key?
I am interested to understand as per bip32, why would anyone share the 'parent extended public key'?


The purpose of sharing the parent extended public key is so that child public keys (and thus addresses) can be derived from it without needing to know about a bunch of addresses individually. This is easier for separated setups where an online computer only has the public keys as the online computer does not need to be constantly refreshed with more addresses to watch for. It can generate the addresses itself.


  In such case, will knowing 'child extended public key' expose 'parent extended private key'?


No. Only knowing both the parent extended public key and a child private key derived with unhardened derivation exposes the parent private key.