in chapter 2.6 : In answering this, two flags will serve you well: -d m and “-p 2”... but make -p 2 usage: make [-BeikNnqrstWwX] [-C directory] [-D variable] [-d flags] [-f makefile] [-I directory] [-J private] [-j max_jobs] [-m directory] [-T file] [-V variable] [variable=value] [target ...] This is FreeBSD 10.3R
This documentation is there for history and actually was removed. FreeBSD does not use pmake anymore but bmake.
But the man page of make and /usr/share/mk/bsd.README still reference this doc: man of page: This manual page is intended as a reference document only. For a more thorough description of make and makefiles, please refer to PMake - A Tutorial. /usr/share/mk/bsd.README: See also make(1), mkdep(1), style.Makefile(5) and `PMake - A Tutorial', located in /usr/share/doc/psd/12.make. I will open a PR for this.