You are close. The omitted phrase is その知識が生かせるのではないか, where か is the question marking particle you must know well.

It says "Can't I make use of the knowledge? (I can!)" as an embedded question, rather than saying "I can't make use of the knowledge".

Similarly, 刺さるのでは in that context means 刺さるのではない（だろう）か, meaning "I wonder if it pricks".

You are close. The omitted phrase is その知識が生かせるのではないか, where か is the question marking particle you must know well.

It says "Can't I make use of the knowledge? (I can!)" rather than saying "I can't make use of the knowledge".

Similarly, 刺さるのでは in that context means 刺さるのではない（だろう）か, meaning "I wonder if it pricks".