Open the Settings app
Tap your name at the top of the screen
View the Apple ID email address under your name
Tap Password & Security if you need more account details
Open the App Store and tap your profile icon to see the Apple ID
Open Messages or FaceTime settings to check the signed-in Apple ID
Go to Settings > Mail > Accounts to see linked Apple ID accounts
Check Settings > [your name] > Media & Purchases for the Apple ID used for purchases