You are correct in general, you can try and report that. Though, one would usually emphasize that meaning with some equivalent of "at all" ie. "אין לי שום תפוח" "אין לי אף תפוח"
or else have it in plural "אין לי תפוחים" as commented above
It accepts "I have no apple". In literal translation this is ok but it's not correct to say it that way in English. It needs to be corrected to "I have no apples".
Ein by itself means "There is no", so you don't need to negate it again with lo. Li means "with me". So the sentence is literally "There is no apple with me".
Why "I do not have apple" is incorrect? What's the reason of emphasizin on 'a' here?
English requires the indefinite article.
It's an error in the English itself, not in the translation.
When the noun is countable, it requires an article: "I do not have an apple".
When the noun is uncountable, you must not use an indefinite article: "I do not have rice".
You can use the definite article "the" in both cases.
This may be why the OP is getting confused whether to use "a"/"an" or not.
Yeah, you simply can't leave out the article in English. I have actually seen excercises where it is left out...
What are the different subjects that can be used.
I can remember לו לך לי
but what else is there?
First person single לי
Second person single לך
Third person single לו/לה
First person plural לנו
Second person plural לכם/לכן
Third person plural להם/להן
The place south of Shechem in Israel called Tappuah - I was wondering is it famous for apple trees?
Not really. It is called that way because it is located near a biblical settlement called also tappuah. Maybe back in their times they had more apples around