Does the word tonbe at the end of this sentence mean to stumble? ...lavi sa a dwol, ou pa janm konn ki kote ou pral tonbe...

It might.
There are two possible meanning for tonbe here:  stumble(fall) or end up.
But based on the first part of the sentence, I would instinctively translate it as:

Lavi sa a dwòl, ou pa janm konn ki kote w pral tonbe.
Life is weird, you never know where you'll end up.
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