My mom lost her iphone. She doesn’t remember the apple id and password. How do I locate the device. All i have is the IMEI number and the cell phone number. A police complain has been lodged but the tracking through IMEI would take time.

Try to recover her Apple ID. It will be the only way you can track it or disable it remotely (assuming Find my Phone is on):

Start the Apple ID recovery process here:

https://appleid.apple.com/#!&page=signin

If that doesn't help, try contacting Apple Account security:

Contact Apple for help with Apple ID account security - Apple Support

The only tool Apple offers for remote tracking is find my iPhone. But for that, yes, you need the AppleID and password to login to iCloud and track it. Find my iPhone must also have been enabled on that phone before it was lost.

iCloud - Find My iPhone, iPad, and Mac - Apple and If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

Good luck. Let us know how it goes.