Hi,
1. Do you know what is this? :cross: The reason it is wrong may be difficult to understand. I'll try to explain.
The underlined part is question grammar and by iself it is a question. Although sentence 1 is a question, the real question part of sentence 1 is "Do you know". The underlined part of sentence 1 is not part of the question, so using question grammar in the underlined part is wrong, That's why question 1 is wrong.
In order for the wording in question 1 to be correct, we would have to make two separate questions out of it because both parts of question 1 have question grammar.
something like..... Do you know? What is this?
2. Do you know what this is? :tick: Sentence 2 is correct because only the real question, "Do you know", has question grammar.
A) I don't know what this is.
B) Do you know what this is?
If it's not clear now, please let me know.
Thanks.