The underneath DOT or Nukta is available at code 0222.
In all possible cases, you should check your laptop manual that should provide information about how to access the numeric keypad buttons. However, if thats not possible, you'll have to rely on your word editor's capabilities.
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If you are using Microsoft Word, you can select 'Insert' Menu and choose 'Symbol', then select the font KF-Kiran or any other Kiran family font and scroll down to end. You'll find the nukta (dot) character in the last row. When you select the character, it should show you the Alt+nnnn code as shortcut key.
Click 'Insert' button to get the character into the document. You can then copy the character and place it after the ka, ja, fa or any other character that you want to describe using nukta.
Also, if you are using any other editor, you can also use "Character Map" (charmap.exe) for similar functionality.
Remember, there is a full stop character that looks similar to Nukta but full stop occupies its own space while nukta operates on the preceding character.