Is there and tool on NT to calculate the correlation between two assets? i.e. ZB ##-## against NQ ##-##.
or even on Interactive brokers?

DaFonseca 

Is there and tool on NT to calculate the correlation between two assets? i.e. ZB ##-## against NQ ##-##. or even on Interactive brokers?

I'm not sure it is possible with NT7.

I personally do this using python and normally data from Quandl or IQFeed.
You can also write an indicator/strategy that exports historical data from NT to a CSV and using other tools measure correlation..

In this case, I could also use excel..

But, another point here,
As a NT subscriber (and IQfeed) can I use IQFEED data out of NT?
How do you do that? directly from its website (using login and password)?

There are several correlation indicators in the download section of nexusfi.com (formerly BMT) for NT.

Click downloads.
Click search below that.
Type correlation.

https://nexusfi.com/local_links_search.php?action=show&literal=1&search=correlation&desc=1&keys=1

Mike