These are skills which may be roleplayed in the GM's presence. Therefore all difficulties, successes and failures involved depend on the GM's discretion.

Some people can detect unlife reliably: Reann hunters, paladins or life clerics of journeyman rank or higher. Success is automatic unless the targets are magically hidden; at that point, it might require Spellcraft modified by the Hide skill. Spellcraft can also yield more detailed information.
In addition, those of lower rank in the organizations above and any bishop or higher of good churches can detect huge numbers of unhidden unlife, but this is much more unreliable and more likely to require Spellcraft rolls with higher difficulties.
Druids and rangers of journeyman rank can detect unlife in natural settings with a roll against Survival

Paladins of journeyman rank or higher can detect outsiders reliably.
Any journeyman or higher in any magic academy can detect outsiders on a successful Lore roll. (difficulty determined by the level of hiding)

Anyone can detect and try to identify magic effects on a successful Spellcraft roll.

Any full spellcaster (Wizard, Sorceror, Cleric, Druid) can try to determine a portal's destination with a Spellcraft roll, the difficulty being determined by the portal. The general information received is the destination of the portal: the location or another plane.
By succeeding at this, you may get to know more, such as how great the distance is on a portal to this plane, and the general type of plane if interplanar. Also, the general type or even the identity of the opener might be gained.

Tracking can be accomplished by anyone with the Search skill. Rangers often get automatic success following easy tracks in nature regardless of skill. Also rangers are the only ones who can track on hard surfaces, like inside a cave.

Druids and rangers can communicate with animals using the Survival skill. The level of communication is limited by the intelligence of the animal. A hawk will have a lot more to say than a worm, but of course communication may be accomplished with both.
The difficulty of the communication depends on the degree of “closeness” of the other entity. It is, for example much easier to communicate with a mammal than with a fish.
The skill can be also occasionally be used to “read” nature to detect ambushes and such from disturbances in one's surroundings.

In general, Lore is used for these with the difficulty depending on your character. Each race and class has things they know better than others and thus the required roll is lower. For example an elf will have much better knowledge about elven history than a dwarf would.

Each class has other forms of professional knowledge; these are usually rolled at 1/level + some Attribute.
A few examples below:
Fighters: siegecraft, militaries, weaknesses of enemies..
Barbarians: weakneses of enemies, raiding tactics ..
Bards: Writing styles, music…
Thieves: lock lore, location of fences..
Clerics: Own church rituals, other churches…