The following example shows how you can add tooltips to grid elements and even do load on demand for their rich content: https://github.com/telerik/blazor-ui/tree/master/tooltip/in-grid.
As for a simple title attribute on the command button - you can Follow its implementation here: https://feedback.telerik.com/blazor/1457593-title-parameter-for-gridcommandbutton (I have added your Vote for it to raise its priority). If tooltips are highly important to your case, you could use your own buttons that have titles in a "regular" column and invoke editing through the grid state: https://docs.telerik.com/blazor-ui/components/grid/state#initiate-editing-or-inserting-of-an-item.
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