You can apply for Dual Citizenship to the USA and almost any other country. Many more people than you might think hold dual citizenship. But the road to dual citizenship, with only a few exceptions, is long, twisting and full of "gotchas".
If you apply for citizenship in another country your US citizenship is automatically revoked. The US does not recognize dual citizenship. You revoke it in writing at a US embassy, outside the US.
Yes, you can apply for German citizenship and be a dual citizen regardless of the fact if your mother was still a German citizen or not.
The US recognizes dual citizenship.
Not unless you renounce your Canadian citizenship voluntarily.
India does not allow dual citizenship. But you can apply and get a passport-like booklet, at the nearest embassy and consulate general, that will allow you to travel to India visa-free.
Japan does not allow dual citizenship; when the person who holds dual citizenship of Japan and another country reaches the age of majority, Japanese officials ask them to surrender one of the nationalities. So, if you have not renounced your US citizenship yet and can apply for (or have) a valid US passport, you do not need a visa to move to the US for work or any other purposes.
I think that if your father was (and/or still is) a US citizen, then you are also a US citizen no matter where you were born. It should be rather easy to get an american passport in the US embassy or consulate in the phillipines for you. As for your mother, I believe that she has to apply for a US visa or "green card" based on her marriage to your father who was/is a US citizen, or thru your US citizenship if you are over 21 years old.
she have to marry again in israeli
By law, the US doesn't recognize dual citizenship (i.e. constitution prevents dual nationality) but somehow it always does recognize it.
Spain has dual citizenship agreement ONLY with Spanish countries of South America, Portugal and Philippines. Other countries have to renounce their citizenship if they can and then become a Spanish citizen- in your case the US allows you to renounce: so you must.
No. The US president MUST have US citizenship only.
Yes dual citizenship is allowed for US citizens.