For a nonmagical pick, you deal (d6+static modifiers) on a regular hit, (d10+static modifiers)x2+2+d10 on a critical hit
Where "static modifiers" includes things like your strength modifier and your weapon specialization damage bonus. This assumes you have the critical specialization for Picks.
CRB page 451 says the following about doubling on critical hits:
"Benefits you gain specifically from a critical hit, like the flaming weapon rune’s persistent fire damage or the extra damage die from the fatal weapon trait, aren’t doubled."
The pick critical specialization grants a benefit on a critical hit, so it isn't multiplied by 2 for the critical. The fatal weapon trait increases all damage dice to d10s, but the bonus damage die is a benefit gained from a critical hit so it also isn't doubled.
As a further example: If your pick is a striking weapon, its base weapon dice are 2d6, so you'd deal (2d6+static modifiers) on a regular hit, and (2d10+static modifiers)x2+4+d10 on a critical hit.