Certain items and runes display this value in their tooltips
Some, but not all, items that grant Heal and shield power will show this value. I was unable to find when these fields were added to their tooltips. As of this edit:
- Staff of Flowing Water
- Mikael's Blessing
- Ardent Censer
Will show your total Heal and Shield power. Example:
Strangely, some items that grant Heal and Shield power do not show this in their tooltip. Examples:
- Chemtech Purifier
- Moonstone Renewer (doesn't grant S&H power on its own, but adds extra depending upon how many Legendary items you have, and shows that added value, not your total)
Additionally, the Revitalize rune, which grants an extra 5% Heal and Shield power, will also show your total in its tooltip:
Old answer, outdated
There is no way to see this value
While it's considered an actual statistic, and has been in the game for almost a full year, this value is not represented anywhere in the in-game advanced statistics menu (available by holding the C key while in-game).
The only way to keep track of how much additional shield/heal power you have is to keep a rough estimate in the back of your mind. It would be really great if this was visible somewhere though...