I have just had a game of the initial scenario in Night of the Zealots and I pulled a Treachery card which had a test, my questions are: can I use a skill card (and it's abilities) from my hand to increase my chances of beating the treachery test? Can I use any card in my hand with the appropriate test symbol to increase my chance of beating the test? Do neither of these things? I played it as the latter as I couldn't find it in the rules (I may have missed it).

You are allowed to contribute any card from your hand that has a matching skill icon. Also, effects on any skill card you contributed may trigger if the conditions apply. For example using the card "deduction" (The seeker card that let's you gather one additional clue while investigating) during a treachery test does not let you discover a clue, since the performed test was no part of an investigate action.

All tests follow the same rules, regardless of what initiated the test. Those rules allow you to commit cards with matching skill icons (and your fellow investigators to commit one such card each), unless something else forbids it (examples include the Peril keyword and some treacheries in Curse of the Rougarou).

Cheers guys, that clears that up.

You're welcome.

Also, each other investigator may play 1 card from hand to add it’s skill icons to a test performed by another investigator at the same location. They may each do this once per test.

The investigator whose test it is may discard any number of cards to add their skill icons to the test.

Only the relavent icons (e.g. agility for an agility test) are counted. The “?” skill icon (wild) is considered to be whatever the tested skill is when it is played.

Skill icons on asset cards that are in play or that are on event cards that are played for their effect, do not count their skill icons for tests.

I think those are all of the general skill icon questions people have when they learn the game. Oh wait, there’s one more: knowledge is the skill that looks like a book, not the one that looks like a head (that’s will). Investigating uses knowledge. The number of times I have taught people the game and then realized they were using will to investigate is almost 100%.

Cheers Ducris, I did know that the book was the knowledge skill, so I'm in that almost category! ?

Thinking back on it, I believe I was in that category too!