Is this claim by Jill Stein accurate?
I'm assuming that she's referring to US veterans, both for the suicide rate and the combined death rate in Iraq and Afghanistan.
Although exact numbers are hard to come by, there is clearly a higher rate of suicides among veterans than the general population and that number exceeds the number of combat deaths in Iraq missions until 2011 and Afghanistan missions from 2001 to the present.
This article from the Military Times notes that:
in 2014, the latest year available, more than 7,400 veterans took their own lives, accounting for 18 percent of all suicides in America. Veterans make up less than 9 percent of the U.S. population. (emphasis mine)
According to wikipedia, total military deaths for Afghanistan is 2,384 and for Iraq is 4,504, which would indicate that the number of suicides in that year alone exceed deaths.
It is worth noting that the studies of military suicide rates is complicated.
This recent New York Times piece goes more into depth with the findings and this Washington Post fact check piece has an in-depth look at the report's methodology and how counting veteran suicides is unclear.
However, they [the authors of the study] acknowledged “significant limitations” in their available data, including people incorrectly identified > veterans in death certificates.
The report does not include some states with the largest veteran population (including California, Texas, Georgia, Arizona and North Carolina), so it is unclear how this would affect the rate.