If you are asking about what address to use for your Schedule C (or other) self-employment activity, then the answer is you can genuinely use whatever address you wish, as long as it is somehow "tied" to your business, in that at least some portion of your business is conducted there.

That said, however, it is somewhat traditional to report the (current) address of your primary physical work location (if you have or had more than one) here.  So, if you've moved to a different state or states during the year, then you would probably want to use the address that is the most recent.

Please note that this can be (and often it is) a different address than the main mailing address on your primary income tax return.  Your primary mailing address is the one that the government -- IRS or state department of revenue -- would use to contact you in writing, if they ever needed to.  It is also the address to which your tax refund will be mailed, if you are getting a refund, and you selected to receive it by mail.  So, when viewed in that light, the location address you input for your Schedule C activity is somewhat less important than your main mailing address.