This is the 2629th most frequent Russian word.
узнают
"They will find out" or "they will recognize."
In this context, 'узнают' means to come to know or learn something new.
Когда они узнают правду, всё изменится.
When they learn the truth, everything will change.
Here, 'узнают' implies obtaining information or results that one was looking forward to.
В следующем месяце студенты узнают результаты экзаменов.
Next month, the students will find out their exam results.
In this example, 'узнают' indicates becoming familiar with or acquiring knowledge about various cultures.