Bootable macOS Mojave USB install disk

Download macOS 10.14 Mojave from the Mac App Store. Once downloaded, you can find the installer at /Applications/Install macOS Mojave.app. Afterwards, launch the Terminal app from the /Applications/Utilities folder.

To create the install disk, execute this command:

sudo "/Applications/Install macOS Mojave.app/Contents/Resources/createinstallmedia" --volume /Volumes/Untitled --nointeraction --downloadassets

Where Untitled is the name of the destination volume, i.e. your USB flash drive. Enter your macOS password to proceed. Sit back, the installer will take a while.