What operation is called morphemic analysis ?

ask – asks

high -higher

In these words the second forms are marked: "asks" is a verb in the third person singular which is expressed by the inflection "s". In its counterpart there's no marker like "s" but the absence of the marker also has grammatical meaning: it means that the verb "ask" is not in the third person, singular number. Such morphemes are called "zero". In the second example the adjective "higher" is in the comparative degree, because of the "- er" while its counterpart "high" is in the positive degree, the absence of the marker expresses a grammatical meaning, i.e. a zero marker is also meaningful, therefore it's a zero morpheme.