How to connect 2010 prius speed sensor for navigation ?

Where did you buy the unit? Ebay? Maybe the seller replaced a broken factory HU with a working aftermarket unit.

If you have a friend with the same model Prius and with factory NAV you could temporarily install your HU in his car. I don't think I'd volunteer my car and I don't think I'd do this even if a friend volunteered.

Otherwise search or spend however long it takes to figure out the install instructions.

If possible I'd return the unit. An aftermarket unit will be as good (better) and will have current maps. You're looking for a factory look? I'd suggest the Advent (Audiovox) unit. Too pricey go with Ottonavi.

You don't care about "factory look". Kenwood, JVC, Pioneer and Sony all have 2DIN units which should work fine.