"Activate iPhone"

The phone can only be activated by your friend typing in his id and password, or by logging into his account via http://www.icloud.com and removing the phone from 'find my iPhone' - until he does so you won't be able to use the phone.

If he can't remember his id then he could try : Apple ID: How to find your Apple ID

Has he tried the link that I gave at the bottom of my above reply to see if that helps him find it ?

Or does he have any of the account's downloads in his computer's iTunes library : Recovering a forgotten iTunes Store account name ?

The activation screen should give a clue as to the account's id, does it not show the first letter of the email address and the '@....' part e.g.

The number of dots that shows after the first character is not the number of letters in the email address, I think that it will always show 5 dots. Does he have an email address starting with that letter with '@....' ?

Does your friend have, or had, a*****@hotmail.com email account ? If the phone was linked to your friend's account in Settings > iCloud then it will be his account that it is locked to

Has he tried the Apple ID: How to find your Apple ID to see if that finds anything ?

And has he checked to see if he has any downloads from that account in his computer's iTunes library ?

If the account is your friend's account then he should try it - has he done so ? If it's his account then only he can potentially find his account and remove the phone from it

Get your money back from your "friend", because the iPhone is useless now.

No without the correct credentials. It cannot be bypassed. Activation Lock is to prevent reuse of stolen iPhone.

Unless your friend can deactivate Find My iPhone, you have a brick .