That's the command in MonoGame.Content.Builder.Task.targets:
<Exec
Condition="'%(ContentReference.FullPath)' != ''"
Command="$(DotnetCommand) $(MGCBCommand) $(MonoGameMGCBAdditionalArguments) /@:"%(ContentReference.FullPath)" /platform:$(MonoGamePlatform) /outputDir:"%(ContentReference.ContentOutputDir)" /intermediateDir:"%(ContentReference.ContentIntermediateOutputDir)" /workingDir:"%(ContentReference.FullDir)""
WorkingDirectory="$(MSBuildProjectDirectory)" />
Any help regarding this is appreciated!