Another tool is strace, just run the thing as
strace gmfsk
add whatever gmfsk args you usually use at the end.
After it stops spewing nonsense, review the last few dozen lines looking
for lines referring to /dev/dsp, and cut and paste them here.
Or, to avoid having to search by hand, just run
strace gmfsk <your-args> | grep -A 10 -B 10 "/dev/dsp"
This will filter out any instance of /dev/dsp, printing the 10 lines
before and 10 after for good measure (10 of course can be tuned to what
ever you feel is appropriate) ...
Chris