Can I include Forex trading loss to form 8960?

Including the loss as other taxable income does reduce your income overall but is not included in your investment income in order to adjust that.  

If you wanted to include the loss in the actual investment as an adjustment to the sale of the investment that you purchased then you would not enter it on the tax return this year but keep the paperwork and enter it as an adjustment to your basis when you sell the investment.  At that point it will be able to help with your investment tax.

@lajax 

A few additional comments:

• In general, forex transactions are covered under Section 988 of the code.  As such, they are treated as ordinary income or loss.  With losses, this can be taxpayer favorable as it reduces other ordinary income and not subject to the $3,000 capital loss limitation.
• As a result, forex taxed under Section 988 is not included with the net investment income groupings.
• There is an "opt-out" capital gains election, but this forum is not the place to discuss whether this is in your best interest.  Additionally, this election is for prospective transactions; no hindsight.
• Depending on your trading level, it may be in your best interest to locate a tax professional that deals with trading and traders.