For example, pretend I am a Stack Exchanger looking to ask a question on Emoji.
I am looking to ask a question on what the main emoji font is.
What would I do since there is no Emoji site?
I suggest using a Google search like:
to see if you get any hits on Stack Exchange sites that have existing questions about Emoji.
If you do, then explore their
help/on-topic pages to see if your question appears to fit well enough to ask it.
If you draw a blank, and are really enthusiastic about Emoji, then check Area 51 to see if there may be an existing proposal that will help you in the future, and if there is not, then consider proposing one.
However, not every question is suitable for Stack Exchange.