If you are interested in the optimisation result from NbClust, you will find it in nc$Best.partition where each number is the cluster number for respective row in the data matrix.
for example
> nc$Best.partition
[1] 1 2 3 4 5 1 3 5 1 1 4 1 4 1 5 1 5 1 4 2
for 20×10 data matrix.
solved How do I know which observations belong to which cluster? [closed]