trickplay location

[HokieRulz]

I can't specifically tell you how to put trickplay images on D:, but can offer one option that in your case would put the trickplay images on your Z: drive since Jellyfin does allow you to store trickplay images at the same location as the media.  Under server settings -> Libraries, find the library that you want to change and click on the three dots at the bottom right of the library, then go to "Manage Library", then find "Save Trickplay Images Next To Media", check the box next to that option, and click save.  It will be a good idea to restart Jellyfin, and I'm pretty confident you will need to regenerate trickplay images.

(I'm not on Win, but a quick google confirms the default trickplay storage location is C:\Users\<Username>\AppData\Local\Jellyfin\config\metadata\library.)