how do I script this jump animation?

The character controller offers a variable isGrounded

var isGrounded : bool Description

Was the CharacterController touching the ground during the last move?

function Update () {
var controller : CharacterController = GetComponent(CharacterController);
if (controller.isGrounded)
print("We are grounded");
}

This variable should solve your problem. However if you don't want to use the character controller component you may use Physics.Raycast

static function Raycast (origin : Vector3, direction : Vector3, distance : float = Mathf.Infinity, layerMask : int = kDefaultRaycastLayers) : bool Parameters origin The starting point of the ray in world coordinates. direction The direction of the ray. distance The length of the ray layerMask A Layer mask that is used to selectively ignore colliders when casting a ray. Returns

bool - True when the ray intersects any collider, otherwise false. Description

Casts a ray against all colliders in the scene.

function Update () {
var fwd = transform.TransformDirection (Vector3.forward);
if (Physics.Raycast (transform.position, fwd, 10)) {
print ("There is something in front of the object!");
}
}

As you can see the layer is an optional parameter. Don't worry about it. By using Physics.Raycast() you can cast a ray down, if something was hit, the function will return true. Just adjust the distance (length of the ray) to your characters size and the return value can be used to see wether you're grounded.