I seem to remember there have been many sentences in the course where the word for "want" has been used without "ko/ka/ki". What could explain this? (I hope my meaning is understood as I cannot type Hindi with my phone)
The को is necessary only with the चाहिए form.
Other forms of चाहना behave like any other verb and don't need the को.
I have explained the difference between using chahiye and other forms of chahna in a comment below.