You should leave them blank.  Unless TurboTax specifically tells you to enter a 0 for an entry, you should always leave them blank.  

Note:  If box 1 (wages) of your W2 is either blank or 0.00, then that will prevent you from electronically filing as the IRS does not allow e-filed W2s with no value in box 1.

[Edited 3.12.18]

I have a w2 with no reportable income. box 12 does have income from a 401K plan. SHould I put zero in Box 1 so I can e-file or should I disregard the w2?

Did the employer send a 2nd W-2 to add information that was missing from the 1st?   If so just add that to the first W-2 and ignore the 2nd.  You cannot e-file a W-2 with no box 1 income.

No. The employer put money into a 401 K that I have with them. I am PRN and have not work any because I am in school.