This is the 17679th most frequent Turkish word.
şükreden
"Şükreden" means "one who gives thanks" or "grateful."
The word 'şükreden' here functions as an adjective describing 'insanlar', meaning 'people who are thankful'.
Hayata şükreden insanlar daha mutlu olurlar.
People who are thankful for life tend to be happier.
The word 'şükreden' is used as an attributive adjective describing 'bir tavır', which means 'an attitude of thankfulness'.
O, sabahları şükreden bir tavırla güne başlar.
She starts the day with an attitude of thankfulness every morning.
Here, 'şükreden' acts as a nominalized adjective, referring to 'a thankful [person]', indicating a general characteristic.