All debian developer tools are available in PureOS. Because we employ the maintainer of git-buildpackage we tend to use git-buildpackage as our main package building tool, but the entire dpkg suite along with debhelper is available. So are all the needed libraries like build-essential and devscripts, et al.
As long as you have a deb-src URL in your /etc/apt/sources.list you can also simply apt source <foo> to get the source of a given package.