Can I export a xpub/zpub/ypub key in bitcoin core? I'd like to add a master public key (any of xpub/zpub/ypub https://support.samourai.io/article/49-xpub-s-ypub-s-zpub-s) for tracking purposes to Sentinel watch-only wallet https://samouraiwallet.com/sentinel.html but I cannot find an option to do this in Bitcoin core (v0.16.1).

Can anyone suggest how this can be achieved?
You cannot. Bitcoin Core does not allow you to import master keys nor can you export extended public keys. BItcoin Core does not use extended public keys since it uses hardened derivation which does not use extended public keys.