Right away. As long as you can open your mouth in comfort, i would not delay getting the root canal. Waiting only creates a greater potential for a dental emergency. A root canal is actually a much easier procedure than the extraction of a full boney impacted wisdom tooth. So don't delay and good luck! and don't forget to get a crown after the root canal is completed! to delay, risks your tooth breaking!
When comfortable. You can have the root canal completed when ever you a comfortable holding open for the time needed for the procedure.
Two options. The first option is to have the wisdom tooth removed and as soon as you are comfortable enough, have the root canal evaluation and therapy. If you are having pain with the tooth that may need a root canal, you may want to have the root canal evaluation and treatment before having the wisdom tooth removed. If the tooth cannot be saved, you can have it removed when your wisdom tooth is removed.