what weapons were used on these ships?
SK L/45 guns
Nassau-class battleship
Each ship carried twelve SK L/45 guns. The wing turrets were Drh LC/1906 mounts, as were the centerline turrets on the first two ships of the class, "Nassau" and "Westfalen". "Posen" and "Rheinland" carried their centerline guns in Drh LC/1907 turrets, which had a longer trunk than the LC/1906 design. The Drh LC/1906 turrets and 28 cm SK/L45 guns were designed specifically for the new German dreadnoughts in 1907. Both mountings allowed for elevation up to 20 degrees, but the LC/1907 mounts could depress an additional two degrees, down to −8. The main battery propellant magazines were placed above shell rooms, with the exception of the centerline turrets of "Nassau" and "Westfalen". These guns fired 666 lb shells, with a fore propellant charge in silk bags and a main charge in a brass case. The guns fired the shells at a muzzle velocity of and they had a maximum range of .

The ships' secondary armament consisted of twelve SK L/45 guns, 
what does the term nassau-class battleship mean? A group of four German dreadnought battleships. who designed them? UNANSWERABLE
wiki:11268371
Nassau-class battleship [SEP] Armament
The vertical triple expansion engines consumed large amounts of internal space that could otherwise have been used for magazines. Without sufficient magazine capacity to support superfiring centerline turrets, designers were compelled to distribute six twin-gun turrets in an unusual hexagonal configuration. Two twin turrets were mounted fore and aft (one on each end), and two were mounted on each flank of the ship. Firing directly forward and aft, the ships could bring six guns to bear and eight on the broadside; this was the same theoretical capability as "Dreadnought", but the "Nassau"-class ships required two additional guns to achieve it.