Currently, it is not possible to copy to clipboard cell values from tables or from text widgets. This is a very useful feature present in Qlikview. There is a threat in the community with workarounds and there are certain extensions with this feature, however it would be much better if this came out-of-the-box.
https://community.qlik.com/t5/New-to-Qlik-Sense/Copy-Cell-Value-in-Qlik-Sense/td-p/1135898