No saber que / si doesn't "normally" trigger the subjunctive. You are declaring what you don't know, so it's seen as a truth:
Ella no sabía que su novio era muy celoso.
She didn't know her boyfriend was very jelous.
No sé si iré al cine después.
I am not sure if I will go to the cinema later.
However, you may see it using the subjunctive if the speaker somehow feels a "rejection, disbelief" about that information. So you may see or hear something like:
Yo no sabía que tuviéramos que rellenar un formulario.
I didn't know we had to fill in a form.
The speaker could have used the indicative here as well "que teníamos que..." but, by using the subjunctive instead, they're presenting that "fact" as something they reject somehow, don't feel confortable with and they detatch themselves from that truth.
I hope it clarifies it.
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