How to know what warranty do I have on my iPhone SE?

You can check on your setting - general to see the warranty or visit website checkcoverage.apple.com by entering your serial number of the iphone

https://support.apple.com/en-us/HT202741

hope this can help you,

Hello ~ Take a look here:

Find information about your warranty or AppleCare plan

~Katana-San~

The standard warranty is one year.