That statblock does not (currently) exist
After reviewing Your Story, Our World, and Paranet Papers (and Dresden Files Accelerated as well), I could not come up with a statblock for a Naagloshii Scion. Here's what I did find:
Your Story p.75 has a sidebar about non-changeling Scions. A highlight:
To get an idea of what you might do to grow your own, start with the Emissary of Power, but also look at the Changeling template—since changelings are the most common type of scion out there.
The Emissary of Power template is with the sidebar on p.75 and the changeling template is before it on p.74.
Despite this, Our World has a Scion template on p.76. The Grendelkin example presented on the same page is probably an excellent starting place (Refresh -18).
The Paranet Papers also have a section on Scions, on p.294; unfortunately it's just Einherjar, which are not a great fit for Naagloshii.
Naagloshii are "statted out" (they're described as nearly plot device-level creatures) at -30 Refresh. There is a note on p.292 that suggests that what you want exists... but gives no information on how to do it. The most notable things are the (expected) True Shapeshifting(Your Story p.177) and Mimic Form(Your Story p.177) powers (along with across-the-board Mythic abilities).
As I recall, there are also lesser skinwalkers, right?
Yeah, mortals who learned the magic that skinwalkers handed down after their corruption. True skinwalkers can possibly sponsor a mortal, probably focusing on the shapeshifting stuff in exchange for corrupt behavior. Either it ’s a unique kind of sponsored magic, or simply an excuse to take those kinds of powers as part of an Emissary of Power character.
So, lesser skinwalkers are just able to shapeshift? Into any form they want to?
Yup, more or less.
DFA has a section with example Scions on p.143 that adds nothing the original works did not.
The DFRPG Forums have no posts with statblocks for Goodman Grey nor Naagloshii Scion. There is one (last post January 2019) that says they intend to, and another that discuses the Rent referenced in his lore.
Take True Shapeshifting and Mimic Form, Evocation and/or Thaumaturgy if relevant, and fill in strength/speed/resistance/recovery with something applicable to your Refresh target.