Line at every whole dollar

On the current version of Thinkorswim, chart studies are only able to display plots. Chart studies are not able to create or modify drawing tools. Which would be required in order to do what you requested.

You can add a horizontal plot on any chart using just one line of code:

plot lineOne = 100;

This will plot a horizontal line at a price of 100 across the entire chart. If you want the chart to display two different lines at different price levels you will need to add a second plot statement and assign it a different value than shown in the example above.

If you want to display 100 horizontal plots on the chart you will need to add 100 separate and unique plot statements to the chart study.

There is another way to handle this. Which is to turn on the chart grid through the chart settings:

Chart Settings --> Appearance --> Gird

This will display dotted lines of the color you select across the chart. But it will also add vertical lines as well.