How do I get the nausea effect command in Minecraft 1.14.2?

How do I get the nausea effect command in Minecraft 1.14.2? I know there's some commands for older versions of Minecraft but none of them seem to work for the latest version...

It really isn't hard to figure out. The syntax has changed since 1.12, but it still has the same concept. The command looks something like this:

/effect give|clear <playerName> <effect> <time> <amplifier>

You can either give or clear effects by typing give or clear. Next, you put in your username. Next is the ID. Instead of typing numbers, a name ID is required (minecraft:<effectName>). Last is amount of time the effect will last (in seconds) and it's amplifier (effect level).

Let's say we want to give the effect to a player named jenny, and we want the nausea effect for 10 seconds without amplifiers. The command will look like this:

/effect give jenny minecraft:nausea 10 0

A full-length guide on using the /effect command can be found here, and the list of possible effects and their IDs can be found here.