Why is 弄 (nòng) in 他终于弄明白了?
弄 = &quot;to make/ to get&quot;
e.g.
干净= clean
弄干净 = make/ get (it) clean
错 = wrong
弄错 = get (it) wrong
清楚 = clear
弄清楚 = make (it) clear

他终于明白了 - he finally understands
明白 (understand) is a verb here

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他终于弄明白了 - he finally figured out
弄明白 = make (himself) understand = figures out