Q.What Kind Of Pest Is This On Elaeagnus Ebbingei Limelight? Are They Harmful?
Besides the black pest on fresh leaves, something white also appeared on the fresh leaves, buds (see second photo). On Elaeagnus pungens I haven’t seen such pests. Nor on other plants. Thank you

Certified GKH Gardening Expert
This does appear to be a pest, and its larva. I am not familiar with the pests in your country, but Elaeagnus can be susceptible to a few pests.
Here are some articles that will help you to treat with infestation, and care for the shrub:
https://www.gardeningknowhow.com/special/organic/what-are-organic-pesticides.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides
https://www.gardeningknowhow.com/ornamental/shrubs/elaeagnus/how-to-grow-elaeagnus-limelight.htm