This is the 2551st most frequent Russian word.
сегодняшнего
"Сегодняшнего" means "of today's" or "of this day" in English.
The word 'сегодняшнего' is used as a genitive form to specify the day, indicating it belongs to 'today'.
Я не завтракаю с утра сегодняшнего дня.
I haven't been having breakfast since this morning.
The word 'сегодняшнего' functions as an adjective modifying 'урока', referring to the lesson of today.
Темы сегодняшнего урока интересные.
The topics of today's lesson are interesting.
'Сегодняшнего' here modifies 'утра', meaning the morning that belongs to today.