I think the Tamil INSCRIPT Keyboard was designed without supporting the question mark: https://en.wikipedia.org/wiki/InScript_keyboard#/media/File:Tamil_keyboard_win.png

Here are some reasons why this should be fixed:
- Inscript keyboard on other platforms (Windows and Linux) insert ? when that key is pressed.
- Chrome OS allowed inserting ? until it broke some time ago.
- Currently ? is bound to nothing, which means pressing that key (i.e. shift+/) is a no-op now. Binding it to ? will make our lives easier without interfering with any other functionality.

- Inscript keyboard on other platforms (Windows and Linux) insert ? when that key is pressed.
I tried the Tamil(INSCRIPT) keyboard on Windows 10. Pressing ? will input "ய".
How can I input ? on Windows 10 with Tamil(INSCRIPT) keyboard?

It has been a few years since I used a Windows machine. When I did use Windows, pressing ? would insert ?. I don't know when that changed.

On both Ubuntu and Debian ? still inserts a ?. (I use KDE, but I don't know if keyboard layouts are dependent on that.)

Please provide a full layout definition which you think is correct for Tamil Inscript Kyeboard. I'm wondering whether there are some other keys, instead of just ?, need to be fixed.

Looking at https://en.wikipedia.org/wiki/InScript_keyboard#/media/File:Tamil_keyboard_win.png I see that many letters are bound to more than one key (both [ and ' are bound to ட, both k and i are bound to க, etc). I don't personally use [ bound to ட, P bound to ச, and o bound to த, but having those bindings don't hurt I guess. ? is the only binding that I used to use, but miss now.

Let me also ask a Googler friend to comment on this issue. He has some informed opinions about Tamil keyboard design.

It's not currently part of the InScript layout, but users would want to type the symbol for Indian Rupee currency: ₹. I wonder if it can be bound to $. Currently it's bound to ர், which doesn't make much sense.

If "$" maps to "₹", is there any other ways to input "ர்"?

> is there any other ways to input "ர்"?

Yes, there is. A letter with a dot above is called an _otru_ (ஒற்று). To type an otru, we have to type a consonant followed by ் (bound to d). To get க், I'd type kd (k = க, d = ்); to get ர், I'd type jd (j = ர, d = ்); to get த், I'd type ld (l = த, d = ்) and so on.

Having ர் available through a single keystroke doesn't follow this pattern. Other otru letters such as த், ற், ச், ட், etc are not available through a single keystroke. ர் is not special in any way, nor is it used more frequently than other otru letters.

Revised the title and make summary here:

 - remap SHIFT+/ to ?
 - remap SHIFT+4 to ₹

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/05a5d24f6e40b546a8b117345b61c2fa77f66eec

commit 05a5d24f6e40b546a8b117345b61c2fa77f66eec
Author: Shu Chen <shuchen@google.com>
Date: Mon Nov 19 13:04:15 2018

Tamil Inscript Keyboard key mapping changes.

Bug:  878949 
Change-Id: Ic6197ff02354d53da9fec1193cd67e073b663d61
Reviewed-on: https://chromium-review.googlesource.com/c/1341436
Reviewed-by: Leo Zhang <googleo@chromium.org>
Commit-Queue: Shu Chen <shuchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609259}
[modify] https://crrev.com/05a5d24f6e40b546a8b117345b61c2fa77f66eec/chromeos/services/ime/public/cpp/rulebased/def/ta_inscript.cc

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/chromeos/overlays/chromeos-overlay/+/4c8562b53691b4f43fe5b68d7c47ac3a257ee012

commit 4c8562b53691b4f43fe5b68d7c47ac3a257ee012
Author: Shu Chen <shuchen@google.com>
Date: Wed Nov 21 13:52:48 2018

This issue should have been fixed in R72 canary 11284.0.0+.

Many thanks for the fix! I am on the stable channel so it'll be a while before I can see the changes in action. But I am happy that this is now resolved.