Looking for the best nightwing story arc or graphic novel
I say start with the collection “Nightwing, Vol. 1: Bludhaven” and then go forward from there. That series from the 90s by Chuck Dixon defined the character.
Titans: Book One (Together Forever) #1-15 (2008-2011)
Optional: Nightwing: The Great Leap (#147-153) This story ran alongside Titans: Together Forever (#1-15), but doesn’t actually cross over with the series.
Honestly, I’d go with the Rebirth run, because it takes all the elements from Dixon’s run and actually writes them well.