What is the reaction force of Friction?
We know that a reaction force is always exerted on the other object.
Also that in Newtonian physics action and reaction forces exist in pairs.
For example, consider the case of friction between the tyre and the road.
If the tyre exerts a force on the road in backward direction, simultaneously the road exerts force on the tyre in the forward direction.
Both forces (tyre on road and road on tyre) are frictional forces and are different aspects of the same interaction.