If you're using the Shaped Character Sheet, you could navigate to the settings (gear) tab and toggle the "Output from this sheet should be:" dropdown to "Whispered to the GM". All Roll Templates output by the sheet will be whispered to the GM, including ability checks. If you just want ability checks whispered, you could ask your players to whisper the built-in macro for ability checks to the GM via /w gm %{Character Name|check_query_macro}, or provide them with a [Ability] macro that does so.