How can I find my Apple ID / iCloud account ID?

Here is how to find your AppleID/iCloud information from both a computer and your apple device:
 

FROM A COMPUTER:
Choose Apple menu  > 

System Preferences, 

then click Apple ID. 

Click Password & Security. 

Your Apple ID will be displayed at the top of the page.

From their you can change your password or click "Forgot Apple ID or password" and follow the onscreen instructions.

FROM MOBILE DEVICE

On your iPhone, iPad, iPod touch or Apple Watch. Tap Settings, then tap your name.

Your AppleID will be displayed under your name.