Arrival by car: From Hermagor via the B111 (Gail Valley Road) or from Oberdrauburg via the B110 (Plöcken Pass Road) to Kötschach-Mauthen, and from there continue towards Plöcken Pass to the Plöckenhaus.
Public transport:
The most sustainable way to travel is by train to Oberdrauburg (coming from Lienz or Villach) or to Hermagor (coming from Villach), theoretically possible.
From Oberdrauburg or Hermagor, you can then reach Kötschach-Mauthen by bus. From here, depending on the season and availability, there is the option to take a call bus or a taxi to Plöcken Pass or to the Plöckenhaus (otherwise, it is several hours of walking from the regular bus station in Mauthen to the start of the snowshoe hike).
Details at - Nassfeld Mobility Information as well as Kärnten Lines Route Planner