How Do I script this?

[Elcron Valdune]

How do I get it to say that I can get a feat when my Ability to cast 2nd-level spells?

the feat reads like this,
Prerequisite: Ability to cast 2nd-level spells.
Benefit: As long as you have an acid spell of 2nd level or
higher available to cast, you can throw an orb of acid as a
ranged touch attack. The attack has a range of 5 feet per level
of the highest-level acid spell you have available to cast and
deals 1d6 points of damage per level of that acid spell.
As a secondary benefit, you gain a +1 competence bonus
to your caster level when casting acid spells.

How do I script it to only pop up when a caster has 2nd lvl spells?

 

[JeffSandmeier]

First, in the custom feat, you would need to add a prerequisite expression (under Expr-reqs) like this:
herofield[tMaxCaster].value >= 2

As far as only showing up when you have 2nd level spells available, that would have to be through a tracker, but I can't find one that actually tracks spell use/spells available.

 

[AndrewD2]

Actually you would need herofield[tMaxSpLev].value >= 2

tMaxCaster is caster level not spell level.

 

[ShadowChemosh]

As far as only showing up when you have 2nd level spells available, that would have to be through a tracker, but I can't find one that actually tracks spell use/spells available.

As its a feat what Andrew gave would simply go on the feat "Pre-Req" so that HL shows a nice warning message about not meeting the Pre-Req.

Its not really worth getting into bootstrap conditions for feats. The warning message is more than enough and easier to work with.