I’m not sure about a Jain symbol or vrata named “Nandhyavrat.” It may be another spelling or a different Jain tradition. If you can share an alternate spelling or a bit of context (where you saw it, which Jain sect it’s from, or what it relates to), I can find the exact symbol and a photo for you.

If you’d like, I can also look up a JainKnowledge page for a related symbol (e.g., Navkar, Ahimsa hand) and share a representative image here.