QUOTE(Vincent6596 @ Dec 27 2024, 06:28 PM)
the monoshock for my feeling is a little bit too soft.
i had tune my monoshock to the max adjustment ad..
how can i doing sag measurement ? what tools is needed to do the measurement ?
okay, understand your suggestion for the brake

you need 2 people to do the sag measurement. All you need is a tape measure, and the tools needed to adjust your preload, in this case your rear monoshock.
There are plenty of resources and videos online for proper sag setting.
What makes you say you need a harder monoshock? unless there is something wrong with the existing monoshock, or you are much heavier than average, the stock monoshock is usually sufficient for most riders.
If you think the rear monoshock is too soft and wobbly, it may have an issue with it, or something else can be off, like tyres, alignment, or maybe you need to ride within the bike's limits.
Even if you do buy a new monoshock, good suspension makers will also ask you for technical details, like spring weights and why your existing monoshock is not working for you so they can customize a set suitable to your requirements.