T1: Does Afghanistan allow for the registration of non-traditional marks (smell mark, sound mark, trade dress, etc.)?

No. 

T2: Can a part of the trademark be a city or country name if that is different from the nationality of the applicant? 

T3: Can a slogan be registered?

Yes, as a trademark or as a part of the trademark. 

T4: Is the use of the trademark on one item sufficient to maintain the protection for all the goods covered by the registration?

No, the goods/ services to be mentioned that need to be protected at the time of filing the application. 

T5: In what way a 'use' of a trademark should be carried out?

Use of a trademark is optional in Afghanistan. (Afghanistan is the first registration country) 

T6: What should I keep in mind to pick a good and protectable name for my new brand? 

Any name can be registered as a trademark except those which have been explained in article number 8 of the Afghanistan trademark law (national flag, symbols of a purely religious nature, pictures of national leaders, words and phrases that could be confused with the government departments of Afghanistan, marks of official organizations, etc.....)

T7: What do the TM, ®, and © symbols mean? When can I use them? Should I use them?

Use of these symbols is optional, ® means a registered mark and can be used after registration of a trademark, © is used for copyright and the copyright law is yet to be enforced in Afghanistan. 

T8: Can a part of the trademark be a city or country name if that is different from the nationality of the applicant?

Yes, a part of a trademark can be the name of a city or country even if that is different from the nationality of the applicant.