Albert Barnes Commentary Ecclesiastes 6:12

"For who knoweth what is good for man in [his] life, all the days of his vain life which he spendeth as a shadow? for who can tell a man what shall be after him under the sun?" — Ecclesiastes 6:12 (ASV)

After him - that is, on earth, in his own present sphere of action, after his departure from here (Ecclesiastes 3:22).