ifIf you mean the "Poincaré groupoid" made by fixed-end homotopy classes of smooth paths of a diffeological space, this is a honest diffeological groupoid. Its construction is contained in Chapter V of the book "Diffeology", exactly the paragraph titled "Poincaré Groupoid and Homotopy Groups" (beginning p.112). If you have something else in mind, be more explicit please.