How to pull another columns information when using a list lookup

probably the best option for you will be to place calculated value control on the form and use lookup() function within it to query for respective transaction number.

there is as well possibility to configure 'additional fields' to be brought in along with primary lookup field when you configure lookup field in the list.

however, disadvantages are that only fields of certain datatypes are supported, and that these additional field are only populated after you submit item to the list.

I was actually able to accomplish what I need through the "Set Variable" workflow action. I first created a "Single Line of Text" workflow variable and within the the "Set Variable" workflow action, I set the created variable to equal "List Lookup". From the drop down that follows, the 'Transaction List' was the "source", "Transaction Number" was the "field", 'Transaction Name' was the "when" and it is set to equal the List Lookup Column on the form. Works like a charm! Thanks for the help though

ah, ok. I understood you want that extra info already in forms.

if you have resolution to your question, mark it answered.

You can just use calculate value , and it works , this is the step:

1. Create a column single txt on your SharePoint list 
2. On nintex form set a calculate value based on lookup in the function : lookup("name of the list","FieldList",parseLookup(NameOfYourcolumntoextratevalueinNintex,true),"FieldTodisplayInTheNewColumn") 
3. Connect the calculate value to your List Colomn 

It works for me !