The dot behind the s should be below it. That's the most 'scientific rendition. You can find it e.g. in Rudolf Meyer's 'Hebräische Grammatik' and in many other scholarly works. Next to this, you can find spellings like 'Qamats' (Langenscheidts Wörterbuch Hebräisch) or 'Kamaz' (Simon Lehrbuch der modernen Hebräischen Sprache).
Transliteration with Q is preferable, because it correctly renders 'Qof' (rather than 'Kaf'). The spelling 'tz' should be avoided as it's normally not used in German transliteration. Now for the vocalization. Qamets is the old form in pausa, Qamats is the conjunct form. In New and Modern Hebrew the latter form is usually used in all cases. 'Kamatz' is a 'popular' transliteration and I wouldn't recommend it. Use Qame/ats or Qame/as.