Answer:
n/(n+1) . . . . n ≠ 1
Explanation:
As written, there is no product. There is ony the sum ...

With appropriate parentheses, this becomes the product of rational functions ...
... (4n)/(4n-4)·(n-1)/(n+1)

_____
At n=1, the product has a "hole" where the denominator of the original expression is zero, so the expression is undefined. Hence the domain of the product must be restricted to n≠1 (as well as n≠-1).