NAME: يونس, Yunus.
Name taken from Verse 98 where there is a mention of “Prophet Yunus”.
٩٨ فَلَوْلَا كَانَتْ قَرْيَةٌ آمَنَتْ فَنَفَعَهَا إِيمَانُهَا إِلَّا قَوْمَ يُونُسَ لَمَّا آمَنُوا كَشَفْنَا عَنْهُمْ عَذَابَ الْخِزْيِ فِي الْحَيَاةِ الدُّنْيَا وَمَتَّعْنَاهُمْ إِلَىٰ حِينٍ
98 Then has there not been a [single] city that believed so its faith benefited it except the people of Jonah? When they believed, We removed from them the punishment of disgrace in worldly life and gave them enjoyment for a time.
But It does not mean that this name is the actual topic discussed in the whole Surah. It is just a reference and mark/symbol to distinguish this Surah from others as is with most other Surahs of Quran. While there are diversified topics discussed in these Surahs.