How could the dogecoin increase the limit of money supply? As far as I know, Dogecoin will only have 100,000,000,000 coins in total. But how can the supply of coins remain uncapped? How could it produce unlimited dogecoins? Is there any specific skill to make the block provide unlimited coins?
The amount of bitcoins is not set by a hard coded limit, but indirectly through the rules of Bitcoin's reward schedule.
Bitcoin's reward started out at 100 bitcoins per block, and halves every 210,000 blocks (approximately four years) until the block reward drops to less than a satoshi when it just stops.

On the other hand, Dogecoin's reward will only halve five times.
Then instead of halving again, it will go to a flat reward of 10k dogecoins indefinitely starting from Block 600,001. Therefore, it will continue to grow slowly without limit.

Also see my answer here: Reward schedule and maximum number of dogecoins?.