The base Sneak Attack rule still applies

Scout uses ordinary Sneak Attack for most of its career. Mobility helps the Rogue reach a legal target or obtain advantage, but the subclass does not create a special qualification method until its 17th-level interaction with Sudden Strike.

Subclass interaction

Scout uses ordinary Sneak Attack for most of its career. At 17th level, Sudden Strike creates a rare opportunity to apply Sneak Attack twice during the same turn, but only if the second Sneak Attack is against a different target. The usual weapon and qualification rules still apply to each attack.

Reaction attacks can still matter

Skirmisher consumes the reaction, which means it competes with opportunity attacks and Uncanny Dodge. A Scout that moves away every time the trigger appears may lose a more valuable reaction later in the round.

Do not double-count subclass damage

At 17th level, Sudden Strike can allow Sneak Attack against a second target on the same turn under the feature's restrictions. It does not permit two Sneak Attacks against the same target during that turn.