Hello, where should I enter my solo 401k contributions in schedule c?

[dmertz]

They do not go on Schedule C.  They are to be entered in TurboTax's self-employed retirement section.  In TurboTax Self-employed, that's under Income & Expenses -> Other Business Situations -> Business Deductions and Credits -> Self-employed retirement plans.  The amount determined here will appear on Form 1040 line 28.