Likely.

People can make out items in the 10-50m range from the ISS. That means the individual trenches probably wouldn't be visible. The were generally only a few meters wide. But the combination of multiple allied trenches, no man's land, and then multiple German trenches generally reached a width of several kilometers.

For example take this picture it shows the trenches near Loos. The area to the upper left is the British trenches the area to the right and bottom is the German trenches. From space it is unlikely that anyone could make out the individual trench lines, but the entire formation would be plenty visible. To get a feel for what it might look like, step back from your screen and squint until the darker trench lines disappear and all you see are the lighter surrounding areas. That'll give you a rough idea what it would have looked like from 400 km up.

Try /r/theydidthemath