1. Where can I find what type of antennas can I use?
2. Is that antenna for receiving signal or sending signal?
3. I connected some antena on my Groove and I made AP but in configuration I didn't have possibility to choose antenna (for example antena a). So I think that my antenna is not compatible.

1. any type that you can attach there.
2. both
3. you don't have to choose antenna in configuration.

1. How can I verify if my antena is working?
2. I have 5-6 LED lights on my Groove 52HPn, but only the first two are on. First one for power and second one for WiFi.
Why other LEDs are not on?
Thanks

Why other LEDs are not on?

As you stated, 1 is for power and the one above it is when a client is associated. I think the signal ones above it relate to when its in another mode, but I will be curious to see someone answer this, as that's the one's I am not sure on myself).