There are many different ways to structure casual questions, and it seems that Bunpro doesn’t cover all of the forms I’ve commonly seen. To verify the information in my notes and to help anyone else struggling with this, please let me know if anything below seems inaccurate or is missing useful context.
これ食べる？- Rising inflection, casual form with no implications
これ食べるの？- Add の, softer and slightly more polite casual form, may add emphasis or seek an explanation
これ食べるか？- Add か, more blunt/direct so may be considered rude depending on tone/context
これ食べる[の/ん]か？- Add [の/ん]か, combination of の and か implications, not as blunt/direct as か and could be interpreted as showing extra surprise or as rude depending on tone/context
これ食べる[の/ん]かい？- Add [の/ん]かい, mostly for yes/no questions, masculine, not as blunt/direct as か but may be considered rude depending on tone/context
これ食べる[の/ん]だ？- Add [の/ん]だ, masculine, not as blunt/direct as か but may be considered brash depending on tone/context