What should I do if I miss my biometrics appointment for I-485?

You can always schedule an info pass to know the status of your case. But I would not worry too much.

EAD(work permit) application was denied. How can I ask for reopen my application?(Pls see explanation for details ideas)

You just refile your EAD application. Good Luck!

I am being transferred abroad for work and want to know how I can avoid having my wife's N-400 denied?

As my colleague has stated there is a specific section of the law that applies to spouses of US citizens stationed abroad in a qualified employment...

You can log onto USCIS to check for processing times. You can also always schedule an INFO Pass. Good Luck!

My question is I fail to naturalization test (understand English ) so can I travel out of USA ?

As an LPR you can still travel outside the United States. Good luck on your next interview.

Why does my I-130 take too long?

You should schedule an INFO pass. You can obtain the status of your case this way. Good luck!

Can a K1 or K3 visa be approved if one of the individual cannot process the documents in their own country?

You can file a fiance visa. Good Luck!

Can I fix my boyfriend papers , we are planning to get married he is 22 and I am 20 , he lives in Mexico and I live in USA ?

As a US Citizen you can file a Family Petition I-130 or you can file a Fiance Visa.

Can I sponsor my niece and her family to the USA, I have no other relatives here?

No you cannot not sponsor your niece to come to the United States.

Can I extend my H-1B visa with a new employer, after being outside the US for 3 years?

Your new employer will need to file a new H1-B petition, which would be subject to the annual cap. Good Luck!