How do I find out how much I made in 2018 separate from my husband. The agi is both of our incomes combined

If your question concerns the 2018 AGI that you have to enter on the 2019 tax return -

If you filed the 2018 tax return as Married Filing Jointly, the 2018 AGI is the same for the both of you.

The 2018 AGI is on the 2018 Federal tax return you filed Form 1040 Line 7

If you need to see how much you made you need to look at your own W2 and any 1099 you received.   But that won't give you the AGI to efile 2019.  There is only 1 AGI on a Joint return.  You enter the same AGI for each of you.

and if you are switching from a joint return for 2018 to married filing separate return for 2019, the AGI you use is the GI on the 2018 joint return