displaying field depending on a boolean attribute

Thank you but i don't manage to understand how I can reach my goal through this documentation . by the way I cannot find the button "Zeige erweiterte Werte"

I assume that I have to add a node but what to do after that, when can I specify me condition ....

I wonder if you could provide me with the main steeps or some tracks to dot that.

thank you in advance.

Adding nodes in general or in an extension is the basic web designer programming technique. This is covered in the basic training. 

I'm glad to assist with more specific questions.

I'v already watched this, thanks.

i still cannot find where I must specify the condition, it seems quite difficult to do that

Add a container, put your visibility condition there, add the Container reference to VI_Common_propertyeditor. Fill as much things as you can, especially PropertyList and EditTable.
Make sure that it is in a iteration or has a cursor assigned.
The easiest way to get that is to add the node container iteration and put everything in there.

Make sure that the non registered user of the registration web has write permission to the email address, if needed.

What I would do without knowing the organization is the following:
- DefaultEmailAddress : if is an external with internal mail required: @external.organizationdomain.com, if not @emailaddress (or empty), if internal @organizationdomain. For those externals that has both i would create a custom column like ccc_additionalmail that if deaultemailaddres has the organization domain you could store it and display it in the webportal as an additional attribute. you could add for that column additionalpermissions to be displayed. Maybe what im not understanding is that you dont want that personalemail to be displayed, if is that the case, leave defaultemailladress to blank and store personal email in another attribute with specific permissions to be read.