How did the people know who the next Imam was? How did the Imams(as) announce themselves as they don't receive revelation from Allah(swt) so how do they know they are the next imam?

The prophet received the revelation from Allah and had all of their names mentioned. There are many narrations to this regard and an especially famous one which Jabir Ibn Abdullah Ansari narrated.

Why is Sperm deemed as Najis while its the source that we and our children will born?

"[O, believers! Remember] When Allah covered you with a slumber To bestow you rest from His Presence And He caused rain to descend on You from the sky, to clean you thereby And to remove from you the impurity From Satan and to strengthen your Hearts and to keep your feet firm Therewith." Quran 8:11

It is narrated -regarding the above-mentioned verse- that what does Allah mean by the impurity from Satan is the semen.

Is it haram to own a dog?

No but the dog should not be kept inside unless it is for a necessity

Can a Christian touch the Quran ? (As in , it is said that Quran can only be touched by Muslims who have done wudhu , so is it the same ruling for Christians?)

The Arabic script requires wudhu to touch. They should be given translations of the Quran instead.

Is Eating Beef Makrooh ?

No

I watched a porn video twice and I'm regretting on that. I'm also doubting my purity. What I can do for the repentance and to come out of this guilt?

Make an intention not to repeat the act and ask Allah for his forgiveness and His help

Can we add ashadunna ameeral momineena and Ali Un Wali ullah in tashahud of wajib namaz

No but according to Ayatollah Sayed Sadiq Shirazi you can add as a mustahab but needs to be worded specifically in a certain way which is different than what you mentioned. He says you can say wa anna ‘Aliyan ni’mat wali. For more see his islamic law book

I recently watched your biography and I can't help to say that I was inspired by how you were guided to Islam. I have a question what affirms your beliefs in Isla. Recently I've been wanting to increase my beliefs in Islam but I don't know how so I thought I should ask you what made you believe in shia Islam so I could increase my beliefs in my own religion.

I've been trying to read books but I can't find the right one. Can you recommend me some books. Also I like to listen to lectures, is there any lectures you liked that you can recommend me even some of your own lectures?

Belief gets strengthened as knowledge increases. Seek knowledge and strive to implement it. Ask Allah to make you firm in your faith and to bring you closer to Him and the path of Ahl ul Bayt (as).

Commentary to the Faith of Shia Islam by Allama al-Muzaffar: Volumes 1 - 4 https://smile.amazon.com/dp/1537536249/ref=cm_sw_r_cp_api_fabt1_Dj9RFb3RYEWPZ

https://www.youtube.com/playlist?list=PLM_dnJgwGVEkzvXs5V_XceKo8-_qV1hqJ

https://www.youtube.com/playlist?list=PLFF83513F53A767BA

Something I never understood is how would people who became bad from negative influences will be judged like for example Yazid. He was really bad but can you blame him? His father was Muawiyah arguably the biggest enemy and hater of the Ahlulbayt so it would be natural for him to do what he did. If Yazid were to have been born in a better household then most likely things wouldn't have been the way they did. He might've been good and even if he were forgiven for most of what he did, what about the sins that he did that affected otherS? Allah won't forgive those until the people he oppressed forgives him. He would have so many but it wouldn't be his fault, it would be his bad influence's fault and now he would have face trial for those. So how will such people be judged?

That is not a valid reasoning. Look at Muhammad ibn Abu Bakr and it becomes clear.

1) What is taqqiya?

2) Is it permissible to hide our beliefs?

1) It is dissimulation. It is when you conceal your beliefs due to an imminent threat.

2) Yes when you are in fear of imminent danger.