MAGI
You will not find anything on a tax return that indicates a MAGI. The MAGI is specific to what is being reported on the tax return and is used for many different reasons.
Go to this website for detailed definitions of MAGI and where and how it is used - https://www.investopedia.com/terms/m/magi.asp
MAGI is calculated differently for different purposes. There are about a dozen different definitions of MAGI, depending on what it's being used for.
What do you need your MAGI for?
In most cases MAGI does not appear on your tax return.