Is this possible to filder by display name (which I made in indexPatterns)? or somehow do something simillar like filter for values which don't have display name for "that" field? it would be great for finding "unknown" values for my field for which I have display name.
Do you mean the custom label you've assigned in index pattern fields editor? If so you currently can't use it in filters in Discover, Visualize, ..., you have to use the field name.