1) if I connect TX, RX and GND and don't connect CP2102's VCC pin to board. Can the MCU still be programmed?

2) If I supply 5DC to the board, can i program my MCU with this wiring connection.

1. CP2102's VCC pin to the VCC of ICSP.
2. CP2102's GND pin to the ground pin of ICSP.
3. CP2102's TXD pin to the RXD pin of the 8051 microcontroller.
4. CP2102's RXD pin to the TXD pin of the 8051 microcontroller.

First, about powering the board:
You can power the devboard from 12V supply OR from USB, not from both in the same time.

Second, about programming:
You can program this MCU with the CP2102 ONLY IF the 8051 MCU has a bootloader already programmed on this MCU chip. If the bootloader program is not present then you must get some appropriate programmer device, for example AVRISP.

 

First, about powering the board:
You can power the devboard from 12V supply OR from USB, not from both in the same time.

I put the CP2102 board into the USB port of the computer and I am supplying 5DC to the board through DC jack. I removed both jumpers of J4 from the board.

Done below wiring

1. CP2102's TXD pin to the RXD pin of the 8051 microcontroller.
2. CP2102's RXD pin to the TXD pin of the 8051 microcontroller.

Should I only connect CP1202 GND to board ICSP GND, leave VCC disconnected of module and ICSP VCC?

I think yes but i am not sure

Edit : Sst89e516rd2, P89v51rd2 MCU has a bootloader

 

I put the CP2102 board into the USB port of the computer and I am supplying 5DC to the board through DC jack. I removed both jumpers of J4 from the board.

Done below wiring

1. CP2102's TXD pin to the RXD pin of the 8051 microcontroller.
2. CP2102's RXD pin to the TXD pin of the 8051 microcontroller.

Should I only connect CP1202 GND to board ICSP GND, leave VCC disconnected of module and ICSP VCC?

I think yes but i am not sure

Yes, it is righ way to do.