Use webform submission id in custom content type I am working on a patient/doctor kind of project where by the patient fills a questionnaire and then the doctor provides a prescription.

I have used webform module to create the questionnaire which the patients would fill, and i have created a custom content type for the prescription.

I need to be able to relate the submission Id of the questionnaire to the prescription but I am not sure how to do it.

Please note that a patient can fill various questionnaires so it is quite important that I use the submission id as it seem as the only unique id available. 

I have tried the node reference module but that only gives me access to the questionnaire not submission id of the questionnaire.
You're right - you can't use references with the webform submissions, because webform submissions are stored in their own special way - they're not actually proper Drupal entities, so they are not properly exposed to other modules expecting to interact with entities.

One thing you can try if you're not too far along in your project is to use the alternative Entityform project.  That should expose form submissions to be referenced.

Let us know if it works!  I haven't used the module myself, I've just heard of it.