Issue spotting was described by a Bar/Bri guy as the grey area surrounding a fact, not pointing out the fact.
Say you have a case which defines assault as "touching" another person in an unwelcome way. Then say you have a man whose boss blew cigar smoke in his face. Note: I have no idea if that's what assault is, since our Torts class didn't cover it.
The issue here is whether the case law that you learned applies to that situation. Do the cigar smoke particles, which do have a physical substance, count as having touched the man's face? Was his boss really assaulting him, when the instrumenet used was not attached to his boss (not an arm, leg, tooth, etc.)? Issue spotting isn't saying, "Oh! this fact is just like X v. Y, it's arguing the grey area--because exam hypos will never, ever line up exactly with cases you read in class.
Summary: See the fact. Find the cases that apply. Then argue how they cases are similar and should apply. Then argue how the cases are different and should not apply. Then come to a conclusion.