You mean from agent interface or Portal? 

From agent interface for exapmle "in the incident ticket the technical users should choose an involved devices". So is it possible to make it as mandatory.

The "Involved devices" is a MANY2MANY relationship, so it's not a field you can mark as mandatory. You can add rules to request at least one relationship to exist, but note the relationship will be added asynchronous, not as part of saving a record, so your logic cannot rely on it for saving the record, only future actions.

Hello,

We have the same requirement.
Sorry for asking stupid questions (but i am new to SMAX). We used to work on Service Manager.

how can we add a rule to request at least one relationship to exist & at the same time the relationship will be added asynchronous.

How the system will ask for a relationship if it's not on saving? when the user will be asked to add a relationship?