Common words:
* Kaffee (coffee)
* Katze (cat)
* Kind (child)
* Kopf (head)
* Königin (queen)
* Körper (body)
* Küchen (kitchen)
* Kunde (customer)
* Karte (map)
* Kiste (box)
* Kalb (calf)
* Krankenhaus (hospital)
* Klasse (class)
* Kleid (dress)
* Knie (knee)
* Kirche (church)
* Kino (cinema)
Less common words:
* Kamel (camel)
* Käse (cheese)
* Kaktus (cactus)
* Kaninchen (rabbit)
* Kantine (canteen)
* Kapelle (chapel)
* Kartoffel (potato)
* Klassiker (classic)
* Komödie (comedy)
* Konzert (concert)
* Krankenwagen (ambulance)
* Krieg (war)
* Kunst (art)
* Kurier (courier)
Nouns with a capital "K":
* Köln (Cologne)
* Kanzler (chancellor)
* Kaiser (emperor)
* Karneval (carnival)
* Klima (climate)
This is just a small sample, there are many more German words starting with "k"!