Source: The Great Interpretation of Dreams (Ibn Sirin)
A nephew (sister's son) in a dream is like a son, indicating support and help.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
A nephew (sister's son) indicates joy and benefit coming from relatives.
Source: Signs in the Science of Expressions (Ibn Shaheen)
A nephew (sister's son) is interpreted as goodness and benefit. Seeing him indicates strength for the dreamer.