Hi,
With the preposition ,I have come across on here,in here
'On here' sounds a bit odd to me,although by using a phrasal verb that includes 'on', you can say things like 'What is going on here?'
You can certainly say things like 'Please come in here'.
Are these correct? If so,why not at here? I usually answer such questions, particularly about prepositions, by saying 'Because that's how English works'. 
I suppose, with a phrasal verb, you could say things like 'What do want me to look at here?'
Best wishes, Clive