You are a long way from requesting or being assigned a duty station. A lot will depend on what you branch when you commission. For some branches you are able to fill out a wish list for duty stations when you are selected for your branch. For some branches, Aviation for example, you will not find out your duty station until you are almost done with BOLC.
While you do fill out a wish list, it is not a guarantee you will get any of the duty stations you put on the list When in ROTC, once you receive your branch and it allows you to request a duty station you can ADSO for a certain station, again it's not a guarantee.
Your Battalion will explain what all this means when you start ROTC or you can talk to the Battalion ahead of time to get more information.