If the phrase "imam mubeen" is understood to refer to a human Imam, such as Imam 'Ali, there is no reason why it has to refer to a human Imam who is presently living since the souls of humans exist after death, and the Qur'an states that martyrs are alive. Although, of course, it could, and God knows best.
As far as your students are from general public who can use the knowledge in good way, and you do not know for sure that they will misuse it in unlawful ways, you are permitted to teach them and give them your skill. If you are sure that a specific group of people will use the skill in unlawful work, then you should refrain from helping them to do unlawful work.
The minimum obligatory knowledge is the basic faith (Tawheed, Adl, Nubowwah, Imamat, Qiyamah) and day to day matters which you need it like Wudhu, Ghusl, Tayammum, Salah rules and what to do when you doubt the number of Rak'ats, fasting, Khums, Zakat, Am Bil Ma'roof and Nahi Anil Munkar, Halal food rules, family rules, Hijab rules, etc.
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