Im told my Grandfather that passed away when I was a young boy was a leader at NYC lodge. How can I investigate this to learn more about my grandfathers life as a mason?

Caine's answer is the best. Contact the Robert R. Livingston library. They have a website with all the information needed to make an inquiry.

They have tours of the building. The guides are very knowledgeable and resourceful. I'm sure they will be able to assist.

There is a Masonic Library there also so the information could be there / they maybe able to help. You need to take ID to gain access. We did a tour.