dh_doxygen: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/dh_doxygen - from package: doxygen

You may install the required package with command apt-get install {package}

Error in other languages:
dh_doxygen: bevel nie gevind nie
dh_doxygen: comandă negăsită
dh_doxygen: comando não encontrado
dh_doxygen: commande introuvable
dh_doxygen: command not found
dh_doxygen: käsku ei ole
dh_doxygen: không tìm thấy lệnh
dh_doxygen: komanda nerasta
dh_doxygen: Kommando nicht gefunden.
dh_doxygen: kommandot finns inte
dh_doxygen: komut yok
dh_doxygen: nie znaleziono polecenia
dh_doxygen: níor aimsíodh an t-ordú
dh_doxygen: no se encontró la orden
dh_doxygen: no s'ha trobat l'ordre
dh_doxygen: opdracht niet gevonden
dh_doxygen: parancs nem található
dh_doxygen: perintah tidak ditemukan
dh_doxygen: príkaz nenájdený
dh_doxygen: příkaz nenalezen
dh_doxygen: команда не найдена
dh_doxygen: командата не е открита
dh_doxygen: 命令找不到
dh_doxygen: コマンドが見つかりません