You can only easily find stuff that is exposed to AngelScript. Look at posts #9 and #16, you have to search for
RegisterObjectProperty calls. For anything else that's not exposed it may require some more understanding of how assembly works, so there's no easy, noob-friendly way.
However I don't know if anything has changed in the meantime, it's been more than a year.
EDIT: So here's stuff for
CTripmineGrenade that you asked for, other people may find it useful. To use them in pdata natives(that require int offset) divide them by 4 (so 1580 -> 395). None of those are exported to AngelScript though, so there's really no definitive tutorial I could write for you how to find them. It's just knowledge, experience, intuition and guessing, the process often differs from finding one offset to finding another one.
Code:
m_flPowerUp = 1580
m_vecDir = 1584
m_vecEnd = 1596
m_flBeamLength = 1608
m_hOwner = 1612
m_hBeam = 1620