Did I translate all of these English question words into Irish correctly?
1. Cé a cheannaigh an leabhar seo?
Who bought this book?

2. Cad a cheannaigh tú?
What did you buy?

3. Cén áit ar cheannaigh tú an leabhar seo?
Where did you buy this book?

4. Cathain a cheannaigh tú an leabhar seo?
When did you buy this book?

5. Cén fáth ar cheannaigh tú an leabhar seo?
Why did you buy this book?

6. Cén leabhar a cheannaigh tú?
Which book did you buy? -- or also in American English -- What book did you buy?

7. Cén méid leabhar a cheannaigh tú?
How many books did you buy?

8. Cén cineál leabhair a cheannaigh tú?
What kind of book did you buy?

9. Cén sórt leabhair a cheannaigh tú?
What kind of book did you buy?

Also, I am not clear about which forms should come after some of these question words. For instance, it is the singular genitive that comes after "cén cineál", correct? Does the same apply to "cén sórt"? Could you touch in this in the response too, please. Much appreciated! :)

Question

Did I translate all of these English question words into Irish correctly?
1. Cé a cheannaigh an leabhar seo?
Who bought this book?

2. Cad a cheannaigh tú?
What did you buy?

3. Cén áit ar cheannaigh tú an leabhar seo?
Where did you buy this book?

4. Cathain a cheannaigh tú an leabhar seo?
When did you buy this book?

5. Cén fáth ar cheannaigh tú an leabhar seo?
Why did you buy this book?

6. Cén leabhar a cheannaigh tú?
Which book did you buy? -- or also in American English -- What book did you buy?

7. Cén méid leabhar a cheannaigh tú?
How many books did you buy?

8. Cén cineál leabhair a cheannaigh tú?
What kind of book did you buy?

9. Cén sórt leabhair a cheannaigh tú?
What kind of book did you buy?

Also, I am not clear about which forms should come after some of these question words. For instance, it is the singular genitive that comes after "cén cineál", correct? Does the same apply to "cén sórt"? Could you touch in this in the response too, please. Much appreciated! :)

Answer

1. Correct.
2. Correct, but you could also say "Cad é a cheannaigh tú?" or "Céard a cheannaigh tú?"
3. Correct, but you could also use "cá" ("cár" in the past tense) instead of "cén áit": Cár cheannaigh tú an leabhar seo?
4. Correct, but "cathain" isn't used everywhere. "Cá huair" or "Cén uair" are alternatives.
5. Correct, but there are also other ways of asking "why?", such as "Cad chuige?", "Cad ina thaobh?"
6. Correct, but you could also use "Cé acu leabhar?", especially when it's a choice between several specific books. This phrase is also useful for asking things like: Cé acu leabhar nó iris a cheannaigh tú? = Which did you buy, a book or a magazine?
7. "Cá mhéad?" or "Cé mhéad?" (followed by the nominative singular) is the correct way to ask "How many?": Cé mhéad leabhar a cheannaigh tú?
8. & 9. "Cén cineál?", "Cén sórt?", "Cén saghas?" are all followed by the genitive singular, to express "what kind/sort OF book, etc.".