I am new to MQ and am trying to make a macro which i need a type cast( or condition not quite sure what it is called. Exampe ${Me.Name}) for group mark NPC would really appreciate any help on this issue.

Depending on how you want to use it...
${Spawn[id #].Mark} - is that spawn marked?
${Me.GroupMarkNPC[#]} - returns spawn id of the group marked NPCs
${Me.RaidMarkNPC[#]} - returns spawn id of the raid marked NPCs