Can I attach Gear to a Sprite token?

Yes, you can attach gear to a Sprite token.

According to Rule 182.1.d, a token unit is a unit and follows all rules for its type unless otherwise specified. Since Sprite tokens are unit tokens, they are valid targets for any effect or action that allows you to attach gear to a unit.

Please note that if a Sprite token leaves the board (for example, if it is killed or returned to your hand), it will immediately cease to exist (Rule 720/FAQ 720). Per Rule 422.4.b, the gear attached to it will not be destroyed or sent to the trash; instead, it will detach and remain at the last board location the unit occupied.