PixelSkills includes a built-in GUI (requiring GooeyLibs to open it) that is used to display skill information to the player opening it. Like many things in PixelSkills, this GUI is completely configurable.
 

# Sets the amount of rows to use in the GUI
# Max of 6
Amount=3
# Sets the title of the menu
Display-Title="&b&lSkills Menu"

Amount: This sets the amount of rows the GUI has in it.
Display-Title: The title set to the menu.

Literally every slot (and amount of slots) in the GUI can be configured, with what's shown in each slot also able to be configured as well. However, as a bit of a forewarning, the GUI uses a chest UI for displaying the the information, and chest UIs have a max supported row value of 6 rows. (6 rows * 9 slots per row = 54 total slots). However, GooeyLibs does not disallow you from setting the value of rows higher than 9. Doing so, though, will cause this weird glitchy looking secondary row of slots to appear between your inventory and actual UI. (Basically, just don't do it). One other important note, the configuration of slots starts at index (slot) 0 and will stop at 1 value less than your max slot amount. (i.e. if you have 6 rows at 9 slots per row, that's 54 slots so your maximum slot is Slot-53, so you would be configuring from Slot-0 to Slot-53)

For convenience (for both you, the user, and me, the developer) the GUI border is branched off in its own section and is configured separately from the slots that show skill information. The display icon used in the border automatically gets its display name set to "". The GUI border slot configuration part of the config file can be found directly below:
 

GUI-Border {
  "ID"="minecraft:stained_glass_pane"
  # Set to 0 if not needed, will error out if not present
  "Metadata"=4
  "Slots"=[
    0,
    1,
    2,
    3,
    4,
    5,
    6,
    7,
    8,
    9,
    10,
    16,
    17,
    18,
    19,
    20,
    21,
    22,
    23,
    24,
    25,
    26
  ]
}

ID: This is the item ID that is used as the border display icon. It supports assigning metadata for it also, directly below. By default, this is set to yellow stained glass panes.
Metadata: The metadata value used for the display icon
Slots=[]: This is a list of integers that represent the slots in the GUI where the border display icon is placed. 

Below the border slot configuration is where the skill display slots are configured, allowing for the user to set the slot, item ID of the item used as the display icon, display name of the icon, and the lore that appears when players hover their mouse over the icon, supporting built-in placeholders for current EXP value, current level, and amount of EXP needed to level up to the next level in that skill.

Important to note that skills are listed by their skill name, not their custom display name (if any are set). (I.e. if you change Breeder's display name to something else, you need to make sure you use "Breeder" in this config file - because "Breeder" is the skill name that PixelSkills recognizes and uses to get information for this skill). The skill display slot configuration section of the config file can be found directly below:
 

Slots {
  # Actual skill name, not custom display name set in the skills.conf
  "Breeder" {
    "ID"="pixelmon:ranch"
    "Display-Name"="&dBreeder" # you can change this to the custom skill name if you want though
    "Lore"=[
      "&aLevel: &c%level%",
      "&aEXP: &c%current%&e/&c%needed%"
    ]
    "Slot"=11
  }
  "Collector" {
    "ID"="pixelmon:poke_ball"
    "Display-Name"="&dCollector"
    "Lore"=[
      "&aLevel: &c%level%",
      "&aEXP: &c%current%&e/&c%needed%"
    ]
    "Slot"=12
  }
  "Darwinist" {
    "ID"="pixelmon:rare_candy"
    "Display-Name"="&dDarwinist"
    "Lore"=[
      "&aLevel: &c%level%",
      "&aEXP: &c%current%&e/&c%needed%"
    ]
    "Slot"=13
  }
  "Fisherman" {
    "ID"="pixelmon:super_rod"
    "Display-Name"="&dFisherman"
    "Lore"=[
      "&aLevel: &c%level%",
      "&aEXP: &c%current%&e/&c%needed%"
    ]
    "Slot"=14
  }
  "Gladiator" {
    "ID"="pixelmon:knuckle_badge"
    "Display-Name"="&dGladiator"
    "Lore"=[
      "&aLevel: &c%level%",
      "&aEXP: &c%current%&e/&c%needed%"
    ]
    "Slot"=15
  }
}

ID: The item ID of the item you wish to use as the display icon. I recommend setting this to an item that can be used to visually represent the skill (Side note: a known issue with this is on Pixelmon Reforged, specifically the Fisherman skill. They apply some default NBT data to the Fishing Rod ItemStack. Granted I could take like 15 minutes to figure out how to remove it, but I don't really care enough since I personally don't use their mod, lol)
Display-Name: Sets the display name of this icon. This could really be whatever you want, but I would recommend setting it to match whatever you are using as your skill display name (either the default one or a custom one you have set). This value supports the use of formatting codes.
Lore=[]: A list of Strings (words, basically) that will get put on the display icon as lore, which displays to the player when they hover their mouse over the icon in the menu. Supports formatting codes.
Slot: Sets the slot number where you want this icon to be at in the menu. Remember that we start at index (slot) 0 so if you want this to be in, say, the 25th slot you need to set the value to 24.
 

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