In multiple line of text column I am seeing the lookup number rather than the actual value

tha't ok, lookup ID is (unique) identifier, not a value.

[this might have changed from version 2.9]

I want to update the value in another list based on the value of Listlookup control but its updating ID instead of value

I assume you are doing update with workflow.

if you have in list A a lookup column to list X, than typically list B contain a lookup column to the same list X. in such a case updating column in list B to lookup ID is fully correct.

if you really need to set lookup value in list B then you have to make 'lookup' to list X by the given ID - it's eg possible directly in update item action

I just did that but I guess there was some error due to which the value was blank,Other way may be to use the lookup function in the nintex form of list B

what kind of error? can you post some details?

you can you lookup function to retrieve and present values from another list in a form. but the function will not update that another list, what was your original requirement.

When I tried to use the action in workflow to fetch the value from ListX by passing the ID and store that value in ListB it was always fetching blank.Finally I used the lookup() in the ListB to get the value