Are you asking about whether it is fixed fully or whether it is developed the right amount?
For fixing you cut off the tongue of your film, put it in a small jar with the fixer you will be using, time how long it takes for the film to completely clear then double the time for fixing
If you cant do that then go by the manufactures nominal time. If the fixer is weak and the film still has the white cloudy silver halides then you only need to put it back into the fixer. You can even do that after the film is dry if you only notice it then..