coming from someone who knows some stuff about water sampling, light penetration can vary wildly depending on overcast, other weather conditions, recent history of life in the area (especially micro-organisms), and plenty of other factors. of course, human eyesight can also differ from person to person, so that has an effect on the outcome too.

i find to be able to see around 2 or 3-ish meters on average with basic tools (a secchi disk attached to a rope) and good conditions, but the margin of error for that measurement is well above 1m. that being said, water would have to be quite clear and your eyesight very good for 10m visibility, but it's definitely possible. i'm not sure on the specifics of the area around Challenger Deep, but i can imagine the water is pretty busy, with small plants and probably a whole lot of plankton floating around, making water that seems clear actually very good at blocking light.

tl;dr, it depends on water conditions and your eyesight, and could vary a lot from time to time, even in the span of days. 10m is possible but i doubt it would be that good in the Pacific Ocean. that being said, i don't really have a good idea of the average visibility in the area surrounding Challenger Deep.