Assuming this is the right part, it appears to be on the left side of the engine case:

 

Try searching site/forums for

service manual scout

You might find links to the 500+ page manual to do all the maintenance tasks on bike including this task.

 

Welcome to the forum. Forum etiquette and rules are that you post an introduction thread before coming cap in hand asking for help.

As stated do a search using ‘Scout Workshop Manual’ and you’ll find the link to it that I (and others) have posted several times referring to it!

 

https://www.indianmotorcycles.net/threads/indianmotorcycles-net-community-rules.361692/

https://www.indianmotorcycles.net/forums/new-member-introductions.48/

 

The Scout has a speed sensor (sometimes called a distance sensor) in the transmission part of the engine/crankcase, very near the output cog of the transmission, where the belt is driven.
Some other Indian Models use the rear ABS wheel speed sensor as the speedometer input.
The Scout has a non-ABS model, while the others all come with ABS. So perhaps the simplest solution for the Scout was to have the old fashioned speed sensor for the non-ABS versions.

Cerialphreak's parts diagram looks accurate to me, there is a cover over the front cog for the drive belt, by the shape of the cover and positions of the belt, you can tell roughly where the cog is under that cover, just move inside of the bike from that point of the cover and you'll find a sensor sticking up out of the crankcase/trans section with an electrical connector, that should be your speed sensor.