For options see here: https://github.com/bozdoz/wp-plugin-leaflet-map#leaflet-geojson-options
The relevant for you may be:
Also, if you want to add feature properties to the popups, use the inner content and curly brackets to substitute the values: [leaflet-geojson]Field A = {field_a}[/leaflet-geojson]
.
You can also write for example:
[leaflet-geojson]{name}[/leaflet-geojson]
If you give me an URL to the website or to the geojson file, I can help more.