How do you see which database on a Server uses most resources
Only some resources can be tracked to databases. IO and buffer pool usage can clearly be tracked to a database:


IO usage: sys.dm_io_virtual_file_stats
Buffer pool usage: sys.dm_os_buffer_descriptors


The query execution statistics (like logical reads) can be attributed to queries, but cannot be associated (correctly) with a database because queries can (and often do) span databases. sys.dm_exec_query_stats is the main entry point for these stats.