"How do I know" the future event or the general present event

1. "Where's Mikey?" "How do I http://dictionary.cambridge.org/dictionary/english/know? He's http://dictionary.cambridge.org/dictionary/english/hardly http://dictionary.cambridge.org/dictionary/english/ever in the http://dictionary.cambridge.org/dictionary/english/officethese http://dictionary.cambridge.org/dictionary/english/day." Here I don't understand the meaning of "how do I know". I mean does it express the future event or the general present event?

2. "Where's Mikey?" He's at home "How do you http://dictionary.cambridge.org/dictionary/english/know?

same question here also?

3. "How do I know that she loves me" Does it express the future event or the general present event Source:http://dictionary.cambridge.org/dictionary/english/how-should-i-know