Wuth Suppressing the Wizard's Handiwork the caster affects only spells cast by himself: as long as he is not subject to fits of amnesia, I would not request spells or rolls for identification of the target. If the magus observed the spell being cast by another and wishes to suppress it with a spell based on the other ArM5 p.161 box guideline, ArM5 p.83 Determining Form of Magical Effect should give enough information.
These are all situations, where the target spell is "easily distinguishable".
Just casting a spell to "suppress a spell cast by another" onto an item or place - e. g. trying to suppress suspected traps on the door of a sodalis' sanctum - should require detailed information (like "I suppress the ReVi effect on the door knob"), an AC to the effect or a means to "sense" it (ArM5 p. 80 The Limit of Arcane Connections).