Sorry, I didn't see your other questions.
"I have one question. How to get the reading for chlorine. Is there testing kit to give the number ?"
As I already stated, the Taylor K-2006 or the TF100 test kits will detect chlorine up to 50 ppm.
"so for my understanding when my morning reading is almost same as night with difference of 1 ppm reading this shocking is done correct ?"
And the water is clear. That's where vacuuming the pool every day comes in. That will clear the dead organics.
"how will chlorine falls back to 3-5 because last morning of this activity it will be 15ppm... do I need to drain the water ?"
You simply stop adding chlorine to the pool until the chlorine falls back to the normal 3-5 ppm level. Then you resume your normal chlorination method. No need to drain water.
"And vacuum can I use robot vacuum ?"
Yes you can, but be mindful of what kind of filters you have in the robot. Most robots come with 2 kinds of filters. The zig-zag or "fan" looking filter will catch bigger particles like leaves, bigger pieces of dirt an debris. The fine mesh looking filters will catch smaller particles like dead algae. So if you're using the fine mesh filters, check them periodically to make sure they aren't clogged.
As you vacuum, what the filter doesn't catch wil be suspended in the water. The filter will catch part of this but sand filters only filter particles down to about 20 microns in size.
To help the filter you can put what is called a "sock" over the skimmer. The least expensive way to do this is to cut the foot part off of a woman' stocking and stretch it over the top of the skimmer basket. But you must check the sock regularly because the dead algae will clog it and reduce water flow to the filter. When you see that it's pretty covered, simply take it off, wash the gunk off of it and put it back on.
Pool supply companies sell a product called a skimmer sock. But if you decide to purchase a skimmer sock just be sure it will fit the smaller skimmer basket that most above ground pools have.
As for buying a test kit that will test for high chlorine levels, the only other suggestion I have would be to take a water sample into the pool company twice a day, once in the morning and again before they close in the evening. But be prepared for them to try to sell you additional chemicals (that you probably don't need)