How can you tell when and if an Endotine has broke through the skin and if so, what needs to be done?

If it is actually coming through the skin you will be able to see and really feel the tips of the implant which are sharp.  If it is coming through it should be removed. The implants can cause some irritation until they dissolve. If they are near a nerve you can get the discomfort your describe.     

Endotine implants in the forehead carry a risk of having the
newly adjusted tissues shift with relatively small movements just after the
operation and before complete healing takes place. This may be what
you’re referring to when you say that the “Endotine has broken through the
skin.” In this case, the implant may
require repeat surgery. Also, you’ve
described some tenderness; this usually goes away after 2 months and the
implants are usually absorbed after 6. You
can assist your healing by avoiding aggravating the area - take a break from
facials as well as leave exercise alone for about 3-1/2 weeks after the
procedure. Hair shouldn’t be washed too vigorously, as well. While it seems like a lot to deal with, this
procedure lowers the likelihood of unsightly or stretched scars or the
cheese-wire effect that occurs when sutures put too much tension on soft tissue
after such a cosmetic procedure.

Occasionally an implant of this type becomes dislodged, but you may just be experiencing an issue related to asymmetric placement. Pain such as you describe can be caused by any implant near a sensory nerve, and usually resolves as the implant dissolves. It won't hurt to get another opinion in your case. A problematic implant can be removed after periosteal fixation has occurred, usually about 3 weeks post op. Good luck!