How do i know if i took a standard deduction or itemized it? For 2018

You will want to look at line 8 of your 2018 Form 1040. Also look at the bubble on the left side of the form next to line 8. This will tell you the amounts of the standard deduction for your filing status. If the amount on line 8 does not match the standard deduction for your filing status, then this means that you itemized. 

If you Itemized Deductions you would have a Schedule A in your return.  How much is on you 2018 1040 line 8?  You may have taken the Standard Deduction instead.  Is it one of these amounts?

For 2018 the standard deduction amounts are:

Single 12,000 + 1,600 for 65 and over or blind = 13,600

HOH 18,000 + 1,600 for 65 and over or blind

Joint 24,000+ 1,300 for each 65 and over or blind

Married filing Separate 12,000 + 1,300 for 65 and over or blind

Or it could be less if you were claimed as a dependent.  How much is on you 2018 1040 line 8?

Look at the return ... if you have a Sch A in the PDF then you itemized deductions.