XVAL of any signal is:
Frequency for AC analysis
Time for Transient
Temp for DC if you sweep temperature.
So if you want to divide some signal by frequency divide that by XVAL of any signal of AC analysis.
1. Here should be expression including VF or IF (It is supposed you run AC analysis if you want divide by FREQ).
2. Why only one quotation mark on the second PORT0. How did you enter this expression?