How can I make a weakaura that tracks the heal/10sec from this gem?

[main sandal]

Is there a buff for it? Then you can track that.

If not, you can do a combat log trigger for the heal, and set the timed hide function at the bottom to 10s.
E.g. as a bar that'd give you a bar that progresses from full to empty over 10s whenever the heal procs, which should be the CD ye?

You'd just have to find out the spell ID of the heal

Make a new aura -> bar
Go to trigger, Combat Log -> Spell -> Heal.
Destination unit player, spell ID what you have there

Timed hide 10s

In the future, you can easily find out the correct thing to track for stuff like that like this:

!etrace

[hearty basin]

See this message #pins message for info on tracking the various game events fired by the API

[main sandal]

!cleu

[hearty basin]

https://warcraft.wiki.gg/wiki/COMBAT_LOG_EVENT

function(event, timestamp, subEvent, hideCaster, sourceGUID, sourceName, sourceFlags, sourceRaidFlags, destGUID, destName, destFlags, destRaidFlags, ...)

You can use this Aura, https://wago.io/CLEU-IN-ETRACE (works fine in all game versions, not just retail), to add the detailed into into the Etrace tool.
For more info on Events and Etrace see #pins message

[main sandal]

It'd tell you what kind of combat log event it is (e.g. SPELL_HEAl), whether you can use dest unit/source unit, the spell ID, etc.

Sometimes things work unintuitively, mby it's not SPELL_HEAL but something else

Always better to check than to guess

Yeah then the combat log trigger isn't correct

[main sandal]

Here

Just do the /etrace stuff and finc out exactly what you need to track