Talk to Moss Druid after the visit to the Marrow and defeat the Bell Beast. She will talk about fruits and task you to gather 3 Mossberry fruits and bring them to her to complete the Berry Picking quest. Here, choose Yes to the “Promise Wish?” prompt for the quest Gather: Berry Picking. In this guide, we will look at all three Mossberry locations in Hollow Knight: Silksong.
All Mossberry Locations in Hollow Knight: Silksong

You will find flying bugs carrying a glowing green orb-like object in their mouth. When you defeat these bugs, you will get the Mossberry. Some places do have Mossberry growing out of the plants; you can just hit them with your common attack to get the item. We have added a map to pinpoint all three Mossberry locations in the game.
Mossberry Location #1
From Moss Druid, turn left and drop down the hole. Now make your way to the ground below and turn right. While the path might appear to be blocked, if you pass the vines, you will get to a small hidden area. Here you will encounter a fly with a Mossberry in its mouth. Hit it a few times for it to drop the Mossberry on the ground.
Mossberry Location #2
Travel to the Bench at the Moss Grotto, head right, and you will eventually get to the spot where you will see a Mossberry hanging off a plant above. Hit it a few times to make the berry drop on the ground.
Mossberry Location #3
Head to the bottom of the Moss Grotto, jump on the small platforms to get to the Mossberry spot. The berry will be hanging off a tree branch above, just hit it to drop the Mossberry.
That’s it, now with all three Mossberries in hand, head back to the Moss Druid and give all three Mossberries to her. You will get the Druid’s Eye crest (Blue Crest) as a reward.
Druid’s Eye: “Amulet of protection formed from Mossberries”
When you take hits, the Druid’s Eye will create green elixir that will form into Silk. Giving away three Mossberries is part of the quest, but you can continue giving her more Mossberries to unlock even more rewards from Moss Druid in Hollow Knight: Silksong.