Does the GS815 Janna need a separate subwoofer?

No. It has two built-in subwoofer units, so bass comes from the bar itself. That saves space but gives less low-end punch than a bar with an external sub.

Can I connect it to a TV?

Yes. It has HDMI, optical and coaxial inputs, plus aux and Bluetooth 5.0. HDMI ARC is not listed, so check your TV's output before relying on the TV remote for volume.

How many speakers does it have?

Six drivers: four 52mm 15W units and two 59mm 10W bass units, for 60W total. That is more drivers than most bars in its class.

Can I use it with a PC and a console at the same time?

You can plug both in, but you switch between inputs with the mode button rather than mixing them. Bluetooth lets a phone connect without unplugging anything.

Is it good for music as well as games?

It handles music fine for casual listening, but the built-in bass units favor games and TV dialogue over deep, tight bass. Critical listeners may want a bar with a real subwoofer.