Provide it with a default workspace.
moving to Model Builder since it is not an Education topic
kapil dev -- please place the model in a tbx file and post it and we'll take a look.
this window appear, when your model need to specify workspace path.
you should check all paths in your model and make sure that all defined.
I think the main problem in your model that there are some processes in model need features or tables but those not specified its workspace.so model check with the user the workspace before execute the model.
Check that you define its workspace well.
thanks
Thanks