Normally a company won't be able to stalk on your Whatsapp communications through HTTPS or the browser as the data is encrypted. However, your company may have installed key logger or screen capture softwares on your computer which could record what you type and Whatsapp messages displayed on your browser.
If the company use SSL intercept proxy (e.g. BlueCoat proxy), the company can capture the whatapps content. You can double check the SSL cert showing on your browser to determine whether the SSL cert is issued by proxy server or valid CA.