Answer
This nucleophile will favor $S_N2$ reactions.
Work Step by Step
1. Use the table of common Nucleophiles on page 216, to compare and determine if this is a strong or a weak nucleophile.
- This is a "$CN^-$" molecule, therefore, it is a strong nucleophile.
** Normally, structures with a negative charge or with high polarity are strong nucleophiles.
2. Strong nucleophiles favor $S_N2$ reactions, therefore, this compound does the same.