It is always good to ask first.
If you’re asking about the reason for grounding both jacks. It’s mainly for redundancy; if one jack fails or comes loose, the other will still be grounded.
The audio path goes from the main board (In and Out – T pads) to the 3PDT switch (Lugs 1 and 7), then to each Jack Tip from (Lugs 2 and 8) respectively. Make sure the T pads on the main board (for both In and Out) are used, since they are the audio path and the pad next to either T pad is for grounding each jack.
If this doesn’t address your question, there are also Beginner Guides below the build documents on the Guides Page that will help.
Also, post that NostalgiTone build in the “Show Off” section.