ssvncviewer: 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/ssvncviewer - from package: ssvnc

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

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