Labhrás, what is your view of: Do lég sé cad a bhí sgríofa?

In case, he read a text headlined "Cad a Bhí Sgríofa" (e.g. an essay about biblical themes) it would be okay

But otherwise it is a difficult question. Indirect questions have a wide range in Irish. And léigh is a "verbum dicendi" which of course should be able to introduce indirect questions.
E.g., "Do léigh sé cad a tharla dhó." would be okay.

But here, he did not read about a question whether something was written or not but he read a text that was written. So, I doubt it is correct.
I would prefer:
"Do léigh sé a raibh scríofa." (He read [all] what was written) or
"Do léigh sé an rud a bhí scrófa." (He read [exactly that] what was written)

But "Do léigh sé cad a bhí scríofa mar gheall ar an rud san. " would be okay.

A good way to check whether an indirect question is possible at all is to ask a polar question ("An...?") with a similar meaning instead.
Do léigh sé ar tharla dhó éinní.
Do léigh sé an raibh éinní scríofa (mar gheall air).


Just to give an example which would be plain wrong because it is not an indirect question:
*Thug sé dom cad a bhí uaim. (He gave me what I wanted). Google Translate suggests this.
It should be:
Thug sé dom a raibh uaim / an rud a bhí uaim.

No, it means "he read what was written". It's from Cnósach Focal ó Bhaile Bhúirne and must be right.

Do chonaic sé cad a bhí ann.

Do you mean that because this potentially answers the question "what was there there?", then this is an indirect question, as long as cad a bhí ann doesn't mean "the actual thing that was there"?

As I tried to say: It depends on the interpretation:
He read something written (e.g. a book, a paper, a library) -> no cad
He read some written content (about something) -> cad



Yes, exactly.

Or in other words: It depends on the usage of chonaic
"Chonaic sé" in the sense of "he found out with his eyes" -> cad
"Chonaic sé" in the sense of "he looked at something" -> no cad

In both cases you can use "what" in English (and, for my part, "was" in German).

Ah! Thank you all for the further clarification!