zsh-dbg binary package in Ubuntu Xenial amd64

 Zsh is a UNIX command interpreter (shell) usable as an
 interactive login shell and as a shell script command
 processor. Of the standard shells, zsh most closely resembles
 ksh but includes many enhancements. Zsh has command-line editing,
 built-in spelling correction, programmable command completion,
 shell functions (with autoloading), a history mechanism, and a
 host of other features.
 .
 This package contains gdb debugging symbols for the 'zsh'
 package.

Source package