You can't know for sure when a trend will end, nevertheless there are a number of clues that you could look out for.
1) Moving average - should you notice price continues to be respecting e.g. 50 interval ma for the past X number of periods, then on the recent retest it broke off the 50ma by a massive margin.
2) A break of structure - Technically in an uptrend we have a series of high highs and lows. If you notice price don't earn a new high and instead close lower and made a lower low, that might be a sign as well.
3) Break of trendline - should you notice price respecting a historic trendline and it is broken by a massive margin, that could mean something as well. One more matter is the level of your trendline, if you always find your adjusting your trendline to be flatter, it's likely a sign of trend transiting into a range market.
Hope that helps!