How to get imi number

Assuming that you have a WiFi+Cellular model iPad, you can see your IMEI and other details in settings:

Settings > General > About > IMEI

If you cannot access iPad settings, simply sign-in to your AppleID account from any computer using a web-browser:

https://appleid.apple.com

Having signed-in, open the Devices tab. Here you will find an entry for every device associated with your AppleID; tap the related entry to see full technical details of the device - including IMEI/MEID of Cellular devices.

More information about finding your IMEI can be found here:

Find the serial number or IMEI on your iPhone, iPad, or iPod touch - Apple Support

if it's a not the cellular model then it does not have an IMEI number

Find the serial number or IMEI on your iPhone, iPad, or iPod touch - Apple Support