Currently in NukeStudio there in no way to change the framerate of imported footage via the user interface. By default the image sequences will import at 24 FPS, based on the setting in Edit>Preferences>Project Defaults>General>frame rate.
You can manually set the framerate of footage in NukeStudio in the Script Editor using Python. Below is the basic command that you need to run in order to set the framerate:
To run this code:
- open the Script Editor panel
- copy and paste the command into it
- press Ctrl + Enter to run the command.
It should then update the framerate of the first clip in the first project, to 25 FPS.
The code works by selecting the project, then the clip and then setting the framerate for that clip to the value defined.
The first square brackets  define the project. As lists in Python start at 0 rather than 1 in the above case this will be set to the first project.
The second square brackets  define the clip from the project, in the above case the first clip.
The end normal brackets () define the framerate FPS value you want your footage set to, in the above case 25.
You can adjust the three numbers to set the framerate of the clip in the project you want, to your desired framerate.