It sounds to me, like you are asking a question about the SharePoint Lookup column, rather than the Nintex Form lookup control is this correct?

If so, then no, SharePoint will not let you reference a lookup column in List B when creating a lookup column to list B from list A.

If you use the Nintex Forms Lookup control then you can select the Lookup column in List B when designing your form in List A. You could then connect this control to a Single Line of Text column rather than a lookup, and write the value of the lookup control to that column. But be aware that if you have the same value selected multiple times in list B's lookup control, this value will show up multiple times in your dropdown.

However, if you are actually looking to select a different column in List B (e.g. Title) and then bring across associated data on that row (which includes your lookup column) then you could use a Calculated Value control and the runtime "lookup" function to pull across that value.

Lily Seifu‌ have you resolved your issue? Is Ryan's answer correct thus you can mark it as "Correct"?

Regards,

Tomasz

Yes, I implement this solution, but is not best solution, I would said that is temporary or palliative. I hope that Nintex improve this feature and function.

Thanks for all.

Fms.