If you are still confused about playing this game, you should try reading this first.

Made by Mimir
Part 1: https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2770467428
Part 2: https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2856595107

When you first arrive in Delta, you can continue to explore and eventually find a beach. This is where you will practice jumping.

Before starting the jump event, you must continue the game story to the stage where you are required to find "Lively fish" in Unertl City. Later you will find a child who is practicing jumping, interact with him, and after that Pienetta will say "I should find a place to practice too".

In order to practice you have to collect swimsuits, because the training will not start if you wear armor and not a swimsuit. Some things that I consider are, the number of team members affects the number of swimsuits that need to be collected. If you do jump training after traveling to Socom City, you only need 1 swimsuit. If your team members are still complete then you must have 4 swimsuits first.
Swimsuit locations are:
1. Left side of Delta Beach
2. Southeast of Meu City, a ruin
3. The third swimsuit is in "Magna" at night behind the water staff in the pot (Thanks to someone in Comment)*
4. South side of the Royal Library, before closing the underground gate, you must first go out and check the pot
*If you know the third position please let me know in the comments.

There are two methods in jumping:
First, you can move normally towards the barrel
Second, you run (Shift) towards the barrel

Secrets you can find:
1. Chest on the left side of the Market in Meu by jumping over the barrels
2. Chest inside the cave on the right side in Nabeach, change into swimsuit and try swimming there

That's all I can give, if there is something missing it means I forgot or maybe I never found it before. Thank you for reading.