In Scotland, I always buy superking cigarettes, and I was wondering if there was a word for this I could use when I travel to Berlin.
This is what a German tobacco producer says:
Die meisten Fertig-Zigaretten werden heutzutage im Format „King Size" verkauft. Dieses entspricht einer Länge von 83 mm. Ebenso gibt es Super-King-Size Zigaretten mit einer Länge von 99 mm. Reemtsma
So it should be safe to ask for super-king cigarettes as you are used to. Not all brands come in super-king size however.
Germans buying such long cigarettes almost always say "100er" ("hunderter"), sometimes "die langen" / "lange" combined with the brand name.
King-Size and Super-King-Size maybe the official names, but it seems that no "end user" uses these words.
The German wikipedia article only references "King size" once, in Germany brands are marketed as "100s" (see for instance https://de.wikipedia.org/wiki/West_(Zigarettenmarke), not as Super King Size.