Asking clarifying questions is a pretty key part of software development. You get a loose requirement the system must do X, you then need to drill into all the details. For this reason I think lots of these coding problems are deliberately under-specified.
One of the big things about being an experienced developer is knowing when things are important. If someone asks me to write a function that returns strings over X characters what counts as a char is going to be whatever the language counts as a char for the length function. Asking about emojis will just lead to a time-wasting discussion about something that doesn't matter.
