want to knock gameobject to the same direction as the projectile

Do you really want to send the blue ball in the same direction as red ball? That would look unnatural. Most likely, if you use rigidbody, you pretty much have nothing to do. You send the red ball and let the engine do the rest.

Though if you are in the case the blue should take the red velocity well I just gave you the answer.

Whatever is the velocity of the red is passed to the blue on collision. If you are translating the red then the vector parameter is the velocity, if you use rigidbody you have teh velocity in

  blue.rigidbody2D.velocity = red.rigidbody2D.velocity; 

no i mean the red ball shoot projectile to hit the blue ball and knock the blue ball to same as the projectile direction that the red ball shoot but i already try with rigidbody would not knock it to the same direction as the projectile that the red ball shoot or maybe i do sth wrong

So your red ball is probably translated with something like:

  transform.Translate(direction * Time.deltaTime);

direction * Time.deltaTime in this case is your velocity.