Here's a link to the study.[1] Since CTE can only be diagnosed by slicing up the brain, and former NFL players only tend to donate their brains to study if they're experiencing cognitive issues, there's obviously a bias in the sample. They tried to adjust for this by looking at rates of cognitive impairment in NFL players who donated their brains versus those who didn't. The ratio varied from 1.8x to 4x depending on age at death.

Unfortunately the number of brains studied isn't large enough to determine whether different positions have different levels of CTE. I'd guess that kickers would have very low risk compared to other positions, as they are rarely involved in collisions. Their stats hint that is the case, but the p-values are ridiculously high due to the small sample size.

1. https://jamanetwork.com/journals/jamanetworkopen/fullarticle...