These recipes are for su.openstreetmap.it, but they can be used for onosm.org (replace the URL where necessary).
Note: jq can be required by some recipes.
curl 'https://api.openstreetmap.org/api/0.6/notes/search.json?q=su.openstreetmap.it&limit=100&closed=0' -o notes.geojson
Then import the geojson file into JOSM using the GeoJSON plugin.
curl 'https://api.openstreetmap.org/api/0.6/notes/search.json?q=su.openstreetmap.it&limit=100&closed=0' |
jq -r '.features[].properties.id | "https://www.openstreetmap.org/note/"+@text'
xdg-open $(curl 'https://api.openstreetmap.org/api/0.6/notes/search.json?q=su.openstreetmap.it&limit=100&closed=0' |
jq -r '.features[].properties.id | "https://www.openstreetmap.org/note/"+@text' |
sort -R | head -n1)