Had breast reduction about 5 weeks ago & there is a white scab at the T-junction. Should I be worried? Is it infected? (Photos)

With respect to bloods supply and healing, the 'T' point is relatively weak and this is the most common place to find some delayed healing following a breast reduction. Most often, these superficial openings will heal on their own. However, a scar revision under local anaesthetic could be considered if the progress is really slow. The Strataderm scar gel is a great product, but it is only suitable for the intact / healed areas of scar. On the open area, I would recommend applying Vaseline, Polysporin or something similar that will help to keep it moist. Remeber to stay in close communication with your surgeon, they would probably like to hear from you and manage this issue directly. 

That white scab looks like you might have some suture (stitch) material preventing that area from healing.   Have your plastic surgeon see you and remove that white scab/material.   Then apply Aquaphor and cover with a dressing like Telfa twice a day until healed.   

Best Wishes!