I am confused by what it is you're requesting. 

You say that you want to Copy the column (aka: get the value), but then you say you are trying to use the Update List Item action to do that? If that's the case, it will not work because that action is only for applying a value to a list item's column(s). As you've already stated, those Additional Fields style columns created by a Lookup are read-only and cannot be updated. 

If you want to get the value of the column and store it in a variable use the Set Variable action or the Query List Action. 

If you require further assistance or if I interpreted your question incorrectly, please let me know. 

Thanks @MegaJerk for responding. 

Maybe I was a little bit unclear. 

In Sharepoint I have made a document library in which I have a lookup column that retrieves extra information called Transportation:Title. I also have made a Copy Transportation as Text column in that same library in which I want to copy the value of the lookup column in. This is because the column itself is not available in Nintex to choose from when I perform the action Update List Item. You have a list of insert reference and the column is not visible. I need to do this because I want to reference it as a quick part in my Word document. 

I have also made a column called Copy Name as Text in Sharepoint where I copy the Name value in. This works with the Update List Item action in Nintex and retrieves copied text in that column from the Name column. I had to do that because the Name column wasn't available as a quick part also in Word.

Now the thing is, I want to do the same with the lookup column but that value is not available to choose from in the insert reference from the Update List Item action. Is there any way how I can achieve my goal? I Hope this makes it more clear!

Thanks!!

Hmm. I will provide an example, but I also notice that you're on Nintex for O365. I feel like it should work regardless, but can't be entirely certain since I know that they changed a lot of the backend regarding how Lookup stuff works over there (it ain't great!)

If this method doesn't work then there are a few other ways we can perhaps go about it. 

First off here is a dummy list with some information pulled down as an Additional Field (highlighted):

Additionally I have also made a blank "SomeText" column to copy those values into but sits unpopulated at the moment. 

Inside of a workflow I have created an Update Item action:

There are a few ways I seem to be able to get the value of the Associated Field in question. First using Value:

Then inserting the Reference from the Item Properties tab:

Or we could perhaps use the List Lookup function:

If for some reason neither one of those works in O365, create a Variable:

And then try to set the value of the variable using the Set Variable action:

This will be like the same deal as before as described above. Try to insert the reference etc.:

If the Set Variable works and you can see the column, now you can just use your Update Item somewhere after the Set Variable action, and use the variable reference instead:

Running the Workflow on the first item results in the SomeText column being populated:

If neither one of those methods works, let me know, and provide some screenshots if you can. Hope it works out. 

Hi @MegaJerk Thanks for your help and extensive answer. 

It helps out a lot!

Your description won't work because I cannot reference an additional lookup column when I want to add an value in the update item action. You have the option to choose from FruitsPrice from item properties and I don't have this option unfortunately. 

I have managed to still get it to work but not in the same way as you described. 

I have created an Set Field in Current Item action and choose the Copy Text Here column as the Field. The Copy Text Here column is where I want to paste the value in. It is the same as your column SomeText. 

As the Source I chose the List where the lookup value initially comes from. 

As the Field I chose the Title field (the one I want to copy in the dummy column).

As the When I chose the lookup value that is referenced in the library from the initial list.

As the source I chose current item.

And it equals the Field of the referenced lookup value in the library. 

I hope it is clear and otherwise I will try to explain furthermore! 

Well I'm glad you at least got it to work! Please mark your comment as the solution if this can be closed.