We'll find out tomorrow who their key witnesses are.

[Dalinar]

is this sentence direct or indirect object noun clause: We’ll find out tomorrow who their key witnesses are.

 

[emsr2d2]

Is this the following sentence a direct or indirect object noun clause?

We’ll find out tomorrow who their key witnesses are.

Welcome to the forum.

Please note that I have changed your thread title. Titles should be unique, relevant, and include some/all of the sentence you're asking us to look at.
Where did you find the original sentence?

 

[Dalinar]

From: https://is.muni.cz/el/1422/podzim2009/DVVP01/um/9401373/Noun_Clauses.pdf

 

[Tarheel]

Two things. One, that site is not mobile friendly. Two, a noun clause cannot be a sentence. (My opinion.)