These words have been deemed as a fabrication, and not a Hadith of Rasulullah (sallallahu ‘alayhi wasallam) by several Hadith masters. Among them are:

‘Allamah Nawawi (rahimahullah) and Hafiz Ibn Taymiyyah (rahimahullah)

These words are actually attributed to the famous Shaykh, Yahya ibn Mu’adh Ar- Razi (rahimahullah), and may be quoted as such. References for all of the above: Al-La-alil Manthurah, Hadith: 100, Al-Maqasidul Hasanah, Hadith: 1149 and Kashful Kahfa, Hadith: 2532.

However, the broader meaning is indeed correct, as one who ponders over the wisdoms of Allah Ta’ala’s creation, can definitely understand His Greatness. There are several such encouragements in the Quran for us to ponder over such. 

This however, does not warrant us attributing these words to Rasulullah (sallallahu’alayhi wasallam).

And Allah Ta’ala Knows best

3 Fatwa links below 

https://hadithanswers.com/he-who-knows-himself-knows-allah-hadith/
https://mawdu.wordpress.com/2016/08/01/he-who-knows-himself-knows-allah/
https://www.islamicteachings.org/forum/topic/23456-fabricated-narrations-stop-quoting-them/#comment-68856