If you have a iPhone 6, the easiest way to find the imei code is to look at the back of the phone. The imei code is engraved to the back of your phone. If you have a protective case you need to remove it to see the imei. See the image below:
The other way is to connect your device to the computer and open iTunes. Then you need to click to the summary tab and you will see the device serial or imei code.
To check the activation lock you can use the serial number (not needed the imei). You can go to this link to check it: http://www.iphonecarrierchecker.com/check-icloud-status/
The alternative way to find the imei of your iPhone 6 is to use iTools. You can download it from the web.
Good luck! Post a comment below if you need more help.