What is an extended public key?
The extended public key (xpub, zpub, ypub; though BB02 & BBApp only support zpub and ypub) is the master public key of a cryptocurrency account. All account addresses are mathematically derived from this key. If you share your extended public key, the service or wallet you share it with can see all the addresses of your wallet, which is bad for your privacy. As the name suggests, it is a public key, meaning you can only view transaction details but not make transactions using an extended public key.
How many extended public keys do I have?
There is one extended public key for each account in the BitBoxApp. Some coins, for example Bitcoin, have multiple address types, which means these coins also have multiple extended public keys.
Do I need my extended public key?
You only need your extended public key(s) if you want to set up a watch-only wallet, or want to add it to an exchange and they use a different address for each withdrawal you execute. In normal use you can completely ignore them and clicking "Verify on device" is not needed at all.
See: How can I generate a watch-only version of my BitBox02?
How to display the extended public key?
In order to access the extended public key of an account, click on the “Account info” button in the upper right corner. You will then see all the extended public keys that are associated with that account in the form of a QR code and the plaintext key below.
In most cases that is just one extended public key, but for example if you use the “unified accounts” feature you will see multiple extended public keys.