Please advise whether the following sentence is grammatically correct. I am uncertain of the word that is underlined.
I spoke with Tom and advised him that Private Clubs/Casinos, are one of the businesses deemed high risk, both locally and internationally.
I am not a teacher.
The slash mark makes your question unanswerable, because it is not English. Use "and": I spoke with Tom and advised him that private clubs and casinos are two of the businesses deemed high risk, both locally and internationally. If you do not mean "private clubs and private casinos", it would be better to put the other one first: I spoke with Tom and advised him that casinos and private clubs are two of the businesses deemed high risk, both locally and internationally.
Even if it the sentence uses just "casinos" you'll find people who disagree, though.
Casions are one type of business.
One type of business is casinos.
It feels horrible to use "is" after casinos.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.