Hi Samson, you can access your PUK code via MyMTN app, when you login to the app, click on the drop down menu, select My Profile, you will see your PUK code. But if your SIM is PIN blocked and requesting you to enter PUK, you need to contact MTN support to assist you with the PUK to unlock your line.
You can contact MTN support via any of these channels:
1. MyMTN App
2. Facebook: @MTNLoaded
3. Instagram: @MTNNG
4. Live Chat: http://bit.ly/2OC5bHz
5. Email: customercareng@mtn.com
6 .WhatsApp: 09033000001