If I have -2 dice pool modifier from sustaining a spell or from Wound Modifiers, does this apply to Body rolls to resist damage?
No, you never apply Wound modifiers to tests about reducing damage (CRB, p.178):
Wound modifiers are applied to all tests not about reducing the number of boxes you’re about to take on your Condition Monitor (such as damage resistance, resisting direct combat spells, toxin resistance, and so on).
The Wound Modifier penalty is also applied to the character’s Initiative attribute and therefore their Initiative Score during combat.
However, according to the rules as written, the dice pool penalty for sustaining spells seems to always reduce your dice pool, regardless of what kind of test you are making:
If you sustain the spell (that is, if you want the effect of a Sustained spell to continue), you take a –2 dice pool penalty to all tests while it is sustained.
The same can be said about other penalties that are not related to how much damage you have taken, such as drawbacks, negative spell effects and critter powers.
There are exceptions to this, but those are explicitly called out:
Secondary effects for characters injured by Electricity damage include a –1 dice pool penalty on all actions and Defense Tests, but not Damage Resistance Tests, for 1 Combat Turn and an immediate Initiative Score reduction of 5.
This is also supported by the wording of the Toughness quality (p. 77):
Characters with the Toughness quality shrug off damage more easily than others. Such characters gain a +1 dice pool modifier to their Body when making Damage Resistance tests.
However, there is a high chance that other modifiers applying to Damage Resistance tests is an error, as this was never the case in previous editions, and the German translation of the CRB (p. 280) clarifies that Drain Resistance is neither affected by Wound Modifiers, nor any other modifiers:
Verletzungs- oder sonstige Modifikatoren gelten für die Entzugswiderstandsprobe nicht..
Roughly translated by google:
Injury or other modifiers do not apply to the withdrawal resistance test
This includes the -2 penalty for sustained spells and other miscellaneous penalties, such as using Astral Perception, or having your attention focused on augmented reality.
There is, however, no mention of this in the latest errata of the core rulebook, so I personally recommend to not apply penalties that are not explicitly mentioning that they apply to Damage Reduction tests, as it could cause strangeness to veterans from previous editions, and it could cause confusion as to what exactly should apply and what doesn't (it's simple if nothing applies).