How does one do the RTW from Karachi when the only flights in and out are from the East (BKK/ HKG)

RTW tickets don't have to go round the world in one direction. It is just the inter-continental order that has to go RTW. Within continents you can go in any direction you want.

thanks. is it possible to do

ASIA - North and south america from Karachi.

Yes - no problem at all. Keep in mind that the rules only allow you two 'stopovers' in Asia if you start from Asia. (A stopover is defined as leaving from an airport more than 24 hours after arrival.) There are apparently very heavy taxes if you buy a RTW ticket in India, so people tend not to do this. I have no idea if something similar applies in Pakistan.

A simplified 8 segment itinerary that is perfectly valid for what you ask is KHI-HKG-JFK-LAX-SCL-EZE-LHR-BKK-KHI. If you follow the link, you will see this shown in the Mileage Monkey (MM) tool. As xONEx tickets allow a maximum of 16 segments for the price of the ticket these days, you can play round with the tool, adding & changing airports as desired. The tool does an excellent job checking if your itinerary is valid within the rules. (For example you are allowed up to 4 segments within each 'continent' you visit, but 6 within North America. MM checks for this, as well as for the more complex rules.)

There is also an excellent planning tool on the OneWorld site. Have fun with trying different options for your trip.

There are 2/3 OW flights in an out of Pakistan depending on how you count:

* isb-lhr on BA
* khi-hkg with a stop in bkk on Cathay

Flights to Pakistan can sometimes be prone to suspension due to the security situation. Not as bad as sri lanka I believe. I think the cathay flights from khi to bkk/hkg (it's actually the same flight) are less prone to issue. Certainly BA suspended flights to isb for a whole after the large bombing a few weeks ago.

BA to islamabad is still suspended. So that leaves only CX.