how do i make my charectar only jump if it collide with a specific object

iam trying to make my Sphere (charectar) only jump when it collide with
for example a cube( a floor ) or so as long as my charectar is colliding with that object that i choose
it will jump
by the way iam using a regidbody
and my charectar is a ball(Sphere)

You can AddForce() or apply velocity in the world y direction when there is a collision ( OnCollisionEnter()) with the specified object:

float jumpForce = 40.0f;

OnCollisionEnter(Collider other){
if(other.tag == “TheTagNameOfTheObjectThat MakesThePlayerJump”){

transform.rigidbody.AddForce(0,jumpForce, 0);
}
}