sshvnc: 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/sshvnc - from package: ssvnc

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

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