Here’s an old post that shows how to debug bigd that gets you the debugs of all the health monitors that are running on the system. The rule of thumb with debugs is that the files get too large and may have an impact on other important services that may need that extra space.
What if you want to enable the debugs for just one pool member to see what’s going on with the health monitor associated with the pool member?
Monitor logging option is a better approach than debugging the bigd for this purpose.
You can find this setting under Local Traffic > Pools > pool_name > Members > Monitor Logging