If you open the layer properties for any layer from QuickMapServices, you will see a link to an attribution guide for the particular data provider.
By following that link you will get to the website for that data provider, where you should also be able to find information about their data management practices.
If you want to view Google satellite imagery from a specific time period, Google Earth Pro for Desktop lets you select the year and season. You could conceivably use this tool to figure out when the satellite imagery in your QGIS project is from.
In practice, it may not be possible to know when satellite imagery on a WMS layer is from. If this is important to your project, you may want to directly download source data, such as Landsat data (which is available for free from the USGS).