Questions & Answers about Li montras la pojnon kaj la genuon.
Because they are the direct objects of montras.
In Esperanto, the thing directly affected by the verb usually takes the accusative ending -n. Here, the person is showing the wrist and the knee, so both nouns get -n:
- pojno → pojnon
- genuo → genuon
The word kaj does not change anything about the case, so both nouns stay in the accusative.
Each ending has its own job:
- -o = noun
- -n = accusative, usually for a direct object
So genuon breaks down like this:
- genu- = the root
- -o = noun
- -n = direct object
The same pattern appears all the time in Esperanto. It is very regular.