When updating the databases sudo must be used – for general usage elevated privileges are not needed – mbn is part of the manjaro-check-repos package.
Install manjaro-check-repos:
sudo pacman -S manjaro-check-repos
Update the mbn database:
sudo mbn update
Query a package:
mbn info <package-name> -q
The resulting command output provides information about the package status in Arch (current), and Manjaro branches: Unstable, Testing and Stable.