The BSD make utility has an option -V that allows to inspect a variable, recursively expanded through a Makefile.
/usr/ports/www/uzbl>make -V PORTVERSION 0.0.0.2010.08.05 /usr/ports/www/uzbl>
The GNU make utility lacks such an option. A bit of web searching gives me the impression that this seems to be a common problem. However there seems to be no intention to change this. Fortunately, there is a work around.
print-%:
@echo $($*)
With this definition you can get the desired effect.
~/Projects/ISILMAR/ports/cvs>gmake print-PORTVERSION 1.12.13 ~/Projects/ISILMAR/ports/cvs>