Short answer
Egg yolks contain some vitamin D and small amounts of omega-3 fats. Hen feed and production conditions can change the amounts, so enriched eggs should be judged by quantified label values.
Vitamin D is mainly in the yolk
Eggs can contribute to vitamin D intake, but a typical serving is unlikely to meet an adult’s full requirement. Values vary across datasets and may be influenced by the hens’ feed and exposure. Whites contain little or none.
Omega-3 enrichment comes from feed
Adding sources such as flax or marine oils to hen feed can increase omega-3 in the yolk. The type and quantity are not identical across products. A front-of-pack ‘omega-3’ statement is less useful than a nutrition claim giving an amount per serving.
Compare with other sources
Enriched eggs can be convenient for people who already eat eggs, but they are not necessarily the most concentrated or economical source. Oily fish supplies long-chain omega-3 directly, while fortified foods or supplements may serve different needs.