What does Jesus mean in Luke 18:8, 'when the Son of Man comes, will he find faith on earth?'

That is a rhetorical question, and rhetorical questions imply you already know the answer; you ask them to make a statement more dramatic, not to get an answer. The answer is no: when He comes back to earth, He will not find faith. Read the rest of the New Testament and it says there must first be an apostasy, and then the man of sin is revealed, and then his little season, and then Jesus comes back on the clouds of glory. An apostasy is a leaving of the faith over the whole world; Matthew 24, Luke 21, Mark 13, and 1 and 2 Thessalonians all say the same thing, that there will be almost no faith left. It makes sense: even in Elijah's day only seven thousand out of a nation of five to ten million had not bowed the knee to Baal. So hang on to your faith; you do not know how precious it is. Those who lose their faith will come and try to make you lose yours, because misery loves company.