It's "make -j8", and unless you have edited the Makefile, it should render all frames.
Here's a nicer version of the "all" rule (it process frames sequentially and should be easier to understand, but all sub-frames required by one image are still done in parallel):
all:
for f in *.dng; do \
$(MAKE) $${f%.dng}-a.jpg; \
rm -f *.npy; \
done
If your inputs are .jpg (same as outputs), I suggest using case sensitivity to tell the difference between inputs and outputs (for example, make the inputs uppercase). For example:
# use *.JPG for input files and *.jpg for output files
%.ppm: %.JPG:
convert $< $@
all:
for f in *.JPG do \
$(MAKE) $${f%.JPG}-a.jpg; \
rm -f *.npy; \
done
That removes the need to run a bash for loop before "make".
When rendering all frames, you may also want to delete the intermediate files. To do so, just comment out .SECONDARY. The *.npy files are an exception, since they are not created with Makefile rules (so "make" won't know it has to clean them up), hence the "rm -f *.npy" in the above loop.