Updating Apps to discover an unrecognized email linked to my account
Did someone help you set up your phone?   

One way this could happen is that someone used their Apple ID to download apps on your phone. 

It could also happen if you restored, updated or migrated your phone on someone else's computer.

The easiest way to solve it is by deleting and downloading them again with your Apple ID.  

The problem is, at least with WhatsApp, that you will lose the data stored in it. You can export conversations by email but that is a very rough way of backing up and it usually leaves out media.

Instagram will ask for your credentials and you'll be ok; Skype will be somewhere around those lines too, but check their support site for specifics —I'm thinking chat history.

As for your data being compromised, it is probably not the case. The person who used this email you don't recognize to download apps on your phone (which is their Apple ID) only has access to a copy of the app on his purchase history —the same copy everybody has access too by the way— not the data inside of it. I would check if this Apple ID was used for some other service on your phone, which could have privacy implications, but that should be asked separately.