Can I deduct Registration fees on my 2 flat and cargo trailers ?

That depends on whether it is for business use or personal.

If the expense is for your business, yes, you can deduct it under Taxes & Licenses in the self-employment section.

If this is a personal expense you may be able to deduct it as an itemized deduction.  Before you try to enter it, check the link at the bottom of this post to see if registration fees are deductible in your state.

If it is deductible in your state, you can enter the amount here:

1. Select Federal from the left side menu.
2. Select Deductions and Credits toward the top center.
3. Scroll down or expand the list to find Cars and Other Things You Own.
4. Expand the section and click Start to the right of Car Registration Fees.
5. Answer the first question Yes and enter your fees on the next screen. 
6. If you have more than one vehicle, click +Add another row to add another vehicle. 

Click here for more information.