Hello
Can I say “variety topics” without word “of” ?
In other words , can I use “variety” as an adjective ?
Thank you in advance for attention .
How about ‘various topics’? 
Thank you , but my question is about a specific expression .
You can’t say ‘variety topics’. Instead, you say ‘various topics’.
Thank you for your attention , but what about “variety shows” in this link :
That’s something completely different. ‘variety show’ is a noun.
‘Various shows’
‘variety of shows’
‘various variety shows’
You’ve got to look at that as one single noun. Read the definition and you’ll see.
Grammatically ‘variety show’ is no different to ‘school teacher’ or ‘pituitary gland’.
Thank you for your valuable clarification .
There are many cases where one noun describes another in a double noun. Variety show, speed boat, garden party, garage sale, language school, book store etc. These have become accepted in the language. “Variety topics” is not such a “double noun.” “Various” in various shows, various topics, various boats, various schools etc. means something else, it just means “a variety of something” a “selection of” etc.
I am a thankful to you .
Does " variation of topics" equal to " variety of topics" in the meaning ?
The two are very similar. ‘Variety of topics’ means ‘many different topics’. ‘Variation of topics’ means essentially the same, but emphasizes the act of changing topics (varying) and so it specifically refers to that action. Examples: She can speak about a variety of topics. If you don’t mind, they would appreciate a variation of topics (meaning please vary the topics).
It’s one of the many weird word groups in English.