dns function is providing a way to map names (a website you're seeking) to numbers (the address for the website).

nothing to do with dns routing.

Its TM unsufficent bandwidth on certain route or certain route path going to destination on long path which cause higher latency (example: destination you wanted to connect is LAX.. TM certain route may get you from KL > SG > Paris > NY > LAX.

Does not have any premium ips range now.
Only depends on your usage, specific ip prefix range will have different routing.
Example
175.X.X.X might have better routing to some network “For this week”
and at the same time 115.X.X.X to the same network might be worse.

But after few days,the situation might be reverse or both getting worse result or both get better result.
So u have to try yourself to see which ip range is better for you at the moment.

And also every night(between 8.30pm to 10pm) TM to some SG network will having sudden spikes or packet lost issue for about 30-60min? (Now is better than 2month ago)

I think the private peering is still existed, but the problem is occurs on TM Unifi end,from what i saw from my smokeping record- the problem just occurs immediately after 9pm.