のだろうかI wonder...

When だろう (the conjugated auxiliary verb) is grouped with か (the question particle), it presents the statement before it as something that the speaker is unsure about. In this way, it sounds similar to 'I wonder if (A)' in English.

To use this construction, the statement before だろうか must be nominalized (turned into a noun-phrase). This is done through the use of の, or なの (in the case of な-Adjectives and nouns).

Despite the grammatical rule relating to nominalization using の (or なの), this part of the phrase is often omitted.

だろうか is quite masculine, so in order to sound more polite/ladylike, でしょうか may also be used instead.

Caution

Although だろうか is quite masculine, it does not strictly mean that でしょうか is feminine. でしょうか may be used confidently by either women or men.

Fun Fact

Like だろう, だろうか may be used to ask a question, or simply to express the speaker's inner thoughts.

However, だろうか is most commonly used to express a personal 'I wonder', in a similar way to かな. Because of this, even if it is used as a question, the listener may assume that you are not specifically looking for an answer from them.