My W2 doesn't have a box 2?

Your income may have been to low to allow for taxes to be withheld.  Your employer uses your W-4 to determine the amount of taxes to be withheld from your income based on what you entered on the W-4.

You will need to ask your employer why there were no federal taxes withheld.

As DoninGA stated, your income may have been to low for taxes to be withheld. As a general rule, if you are filing single, then income up to $12,550 of income is tax free while if you are filing as married jointly, then total income combined up to $25,100 is tax free. 

If you feel, your income is above that threshold or if you in general would like taxes to be withheld during the year, then you will have to file a Form W4 which is usually available on the payroll information website of your company.

I have attached a section of Form W-4 below. I have highlighted the area where you can enter any amount which you would like to withhold from each paycheck.