Mods might want to move this to the general part of the forums instead of the trip reports.
Yes, you can certainly request a specific server just by calling
DCL and having them note it on your reservation. Keep in mind, that serving teams do get mixed up so if you liked a particular duo, they may no longer be together. It's best just to request one person that you want - just give DCL their name and country of origin, and they should be able to figure out who it is. If you can't remember and kept your paperwork from the cruise, you can look up their full names on the part of the tip slips you got to keep.
If you are going to request a server, it's likely best to make that your only request. If you also request a specific dining rotation or something else, DCL may not know what is most important to you and may not grant any of your requests. By limiting your requests to one, they have much more flexibility to try to make it work for you
You won't find out if your server request was granted until your first night at dinner, unless you go to the area marked dining changes after you board to inquire. If your request wasn't granted, you can ask again there if it's possible, but sometimes crew members that you may have had and enjoyed in the past may have been promoted, on leave or no longer working on the ship.
Hope this helps!
Aby