判断・推量N3
〜だろうか
I wonder if... / would it...? (self-question)
Structure
句子（普通形）+ だろうか
Explanation
The questioning/self-questioning form of でしょう, "I wonder if...". Can also be a rhetorical question (本当に大丈夫だろうか).
Examples
このまま進んでいいのだろうか。
I wonder if it's all right to keep going like this.
彼は本当に来るだろうか。
I wonder if he'll really come.
Note
だろうか expresses self-doubt or a rhetorical question ("how could...?").