OK, a lot of people have been asking & complaining about skill training for their employees, especially pilot training. This is my current understanding of how things work (I am not a DEV: all info here is gleaned from assorted forum posts plus gameplay experience!)
Experience gain can happen in 2 ways: the easy way & the hard way. The easy way is fairly simple: use seminars. These train 1/3 of a star of experience per seminar, & can be easily & cheaply bought from any station shop (shops restock fairly regularly after some time), so gaining a 2 star <whatever> employee is fairly quick with a little station-visiting & purchasing. Above 2 star (ie to train to 3 stars) seminars you’ll need to start looking for mission rewards or rely on random loot/lockbox drops (very rare); fortunately the lower tier seminars are fairly common as basic faction/war mission rewards (eg for satellite repair work etc), if not for unaffiliated missions. For higher-tier (lvl 3+) seminar rewards though, you may well have to perform some non-trivial task(s) for an affiliated faction
The other way for NPCs to gain experience is for you to use them to complete tasks assigned to them: with each successful task completed, the NPC gains some experience (XP). With this mechanic in mind it’s easy to see why (eg) your station managers are gaining management skill like crazy (unless you’ve been a complete idiot WRT setting up their station & assigned orders ofc); likewise any ship with crew that’s assigned to engineering & often suffers damage (even minimal) will lvl that crew’s engineering skill very quickly (eg miners). Morale gives an incremental boost to all skills & increases passively over the time that employee is employed*; marines gain their experience from successful boarding ops* ofc. See https://forum.egosoft.com/viewtopic.php?p=4945274#p4945274 for a quick summary
* (See below for more accurate linked info; I'll summarise it here when I get a round tuit)
So now we come to pilots: the bane & essential element of many an X4 player’s strategic as well as tactical plans! Piloting skill is crucial in many ways: it increases the combat capability of the NPC craft (eg main gun/turret accuracy & heat management), plus its manoeuvrability (crucial in a L/XL ship, but also important for an M frigate or even an S fighter/bomber), while decreasing time taken for the NPC pilot to make decisions (eg which direction to point when travelling, manoeuvring in combat, or performing docking/gate manoeuvres*).. the overall result for higher-skilled pilots is less travel time taken for that ship/fleet to traverse to where you want them, & better effectiveness once they get there
* Those gate lights aren't for show: they indicate 'safe passage' for the relevant ship traversing the gate. While it's unusual in X4 for gate transfers to be fatal if heading the 'wrong way' (look at which way the gate lights are 'flowing'), capship collisions can still happen if you force them to travel against the indicators. Fortunately NPC pilots always obey those indicator lights: BE WARNED!
So, how to train them efficiently? Well, there have been a number of mods created to get around Egosoft’s curious blind spot WRT pilot experience gain (eg https://forum.egosoft.com/viewtopic.php?f=181&t=424312#p4929370 which looks v interesting & not particularly unbalancing or immersion-breaking IMO), but for a pure vanilla game there are some things you can try after levelling pilots to max with basic & 1-star seminars:
There’s a forum thread here: https://forum.egosoft.com/viewtopic.php?p=4934113#p4934113 explaining how to take advantage of this last method in more detail, but BE AWARE that it’s in the /Spoilers forum, & links in its following comments may take you to places you don’t wish to know..
Many thanks to Werit Gaming for providing those talkthrus!
As always, this is WIP so don’t expect it to be entirely accurate, especially as & when new versions/fixes are released! However, please leave comments/observations below & I’ll try to incorporate them to make this guide more accurate for current or future game versions/fixes