Generally when you can construct a sentence with 'whose', 'of whom' and 'about (in final position)' there are chances it is translated with 'dont' in french. - the boy I told you about : le garçon dont je t'ai parlé - the boy whose homework is missing : le garçon dont la copie manque - the boy of whom you know the parents / whose parents you know : le garçon dont tu connais les parents This is the easy hack, yet it's possible you'll find sentences that do not enter this pattern, 'dont' covers a wide variety of constructions in english.

An easy hack is that the verbs followed by "de" call for "dont". Je parle de cette voiture -> Voici la voiture dont je parle. Je parle à Bob -> C'est à Bob que je parle (here, there is no "de" -> so there is no "dont") I don't know if that rule always works, so be careful...:)