-НИК, -НИЦА
These suffixes are rarely stressed. Stress falls on the syllable just to the left of this suffix:
учебник text book
противник opponent
затейник entertainer
праздник holiday
ножницы scissors
лестница steps
разница difference
Note: The word страница does not have the suffix -ниц-; the root is стран-.
The compound suffix -венник is also unstressable:
путешественник traveler
There are a few exceptions:
ученик
Since these latter are so rare we will just mark them when they are encountered. You can choose to memorize the word with its stress if you think you will need that word again.