What is an example of dramatic irony when Bruno encounters Pavel in The Boy in the Stripped Pajamas?
There may be some confusion in your question. Dramatic irony occurs when the reader/audience knows something about the situation or characters that the principle character does not know: we know what is going to happen or what has happened or what relationship exists between others when the central does not know this. "Encounter," without further detail, implies an initial meeting between characters.
When an initial encounter occurs early in a work, there is usually not anything to be known by the reader that the character(s) doesn't know. When Bruno first encounters Pavel, he recognizes him as the man who peels vegetable and is a "good waiter."
There is situational irony when Pavel is order by Kotler to find a "suitable tyre" for Bruno. Here Kotler calls Pavel a "filthy----," the word is never filled in in the text. Yet Bruno recognizes that it is Kotler who is filthy and "nasty" so he ironically wants to save Gretel from him.