Why is one side/drop out of my fork like this?

[sefton1275gt]

 

[widowmaker]

Are there 2 holes in it ?

 

[averagebiker]

Looking at the picture there are and they are both threaded.

 

[Double-E F]

To install disc brakes?

 

[novocaine]

It's not a disc mount.
more likely to be a pannier mount and a mud guard mount.

 

[sefton1275gt]

2 holes. After a quick Google it looks like there are other Univegas with this same feature.