common fragmentation mechanisms in mass spectrometry

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Two common types of fragmentation in mass spectrometry are charge site-initiated and radical site-initiated fragmentation. In charge site-initiated fragmentation, a bond directly to the charged atom is broken to afford a new fragment cation and a new fragment radical. In radical site-initiated fragmentation, a bond that is remote (often adjacent) to the radical cation atom is cleaved to form a new fragment ion and radical. The fragmentations can occur either heterolytically or homolytically, and multiple possible fragmentations are often possible from any given parent ion.

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At 5.05 time stamp, why negative charge came near lone pair???

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That negative charge is the formal charge on the carbon atom - the carbon atom that bears the lone pair. Keep in mind that the carbon also has a C-H bond (not shown), so the carbon has three bonds (one to the carbon chain, one to oxygen, one to hydrogen) and a lone pair. That gives it a formal charge of -1.