Meaning of か in ーだかわからない

Question

I found this sentence:

その晩、夢を見た。いつの事だかわからない。けれども覚えのある光景があった

What is the meaning of that か in 「事だかわからない」？ Is it there to add a "uncertainty" nuance? or is it something else?

Answer 1

This か is a question marker, and いつの事だか is an embedded question.

• Usage of か after a clause?

As the above link says, it's okay to have だ before か in embedded questions, and the が between the noun and わかる is usually dropped.

• いつのこと(だ)?: "When was it?" (an ordinary question)
• いつのことだか: "when it was" (an embedded question, now a noun clause)
• いつのことだかわからない: "I don't know when it was"

その晩、夢を見た。いつの事だかわからない。けれども覚えのある光景があった。
I saw a dream that night. I don't remember when I saw it, but there was a scenery I do remember.