I checked, there was no officer of this name in the Prussian army.

Demmin lies in the province of Pomerania.

Recruited from this province were the

1. Pommersches Infanterie-Regiment [No. 2]
Kolbergsches Infanterie-Regiment [No. 9]
14. Infanterie-Regiment
20. Infanterie-Regiment
21. Infanterie-Regiment
1. and 2. Pommersches Landwehr-Infanterie-Regiment

Th 20th line in 1815 was part of the garrison of Mainz and later took part in the siege of Landau.

The other four line regiments served in 2nd army corps (Ligny and Waterloo), the two Landwehr regiments in 4th army corps (Waterloo only).

If he was taken prisoner, he probably was taken at Ligny on 16th.

I don't know of any Prussian prisoners at Waterloo. But it maybe could have happened temporarily, during the fight at Plancenoit.

On 15th, only 1st army corps was involved and lost prisoners, but none of the above regiments was part of this corps.

Most of the Prussian roll calls were destroyed when the Prussian military archive was bombed in the beginning of 1945, so it would be real luck if a list of one of these regiments still existed and Witt would be found in it.

If the anchestor was in the artillery or cavalry, he will be even more difficult to find, if he can be found at all.