Attribution
Attribution is the credit line shown on a map that names the sources it was built from. For maps built with OpenMapTiles it is not optional. The OpenStreetMap data is published under the Open Database License, which requires you to credit the source. The OpenMapTiles schema is published under CC-BY 4.0, which requires you to credit the OpenMapTiles project as well.
What you have to credit
A map built from OpenMapTiles normally carries two credits:
© OpenMapTiles © OpenStreetMap contributorsThe first credits the schema and the tiles, the second credits the underlying data. If you serve the tiles through a hosted maps API, that service may ask for a credit of its own as well.
Where the credit goes
The credit belongs on the map itself, in a place a reader can find without hunting for it. Every map library has a control for this, usually anchored in a bottom corner, and most of them accept HTML so you can link each credit to its source.
If the map is too small for a visible credit, put it next to the map or behind an information icon, but keep it on the same page.