A Form 1099-R with code J or code T should have a blank box 2a. Only a regular distribution reported with code Q in box 2a should have a zero in box 2a and, being a qualified distribution, is not reportable on Form 8606 at all. Qualified distributions will appear only on line 4a of Form 1040.
If reported with code T and the distribution was made more than 5 years after the beginning of the year for which you first made a Roth IRA contribution, the distribution is again a qualified distribution and not reportable on Form 8606.
