Where can I find my EIN?

An EIN is an Employer Identification Number issued by the IRS to a Business Entity.

(NOTE If you are a Sole Proprietor, you do not need to apply for an EIN. You do not have a business entity, you are operating your business as -you- therefore your business activity is reported under your social security number)

If you are an LLC, Corporation or a Partnership, these are business entities. You have formed a business entity that is separate from -you- the individual. Your business entity should apply for and have an EIN (a tax ID for your business) so that all of your business activity is reported under your business and its EIN. You will need your EIN to open a bank account in the name of your business entity. 

If you have lost or misplaced your EIN or EIN verification letter, you can easily request a new copy from the IRS by calling the Business & specialty Tax lin at 800-829-4933. An assistor will ask you for identifying information and provide the number over the phone. You may also request a replacement letter if needed.

For more information see https://www.irs.gov/businesses/small-businesses-self-employed/lost-or-misplaced-your-ein

See also What should I do if someone asks for my W-9?