To grease the knuckles:
undo that square headed bolt and put a cable tie in as a dipstic.
Put half full of grease. Not full, no pressure! Move the knuckles and use the truck and monitor result.
Check your axle oil! (I saw cases of bone-dry axles, where sellers had removed the oil to hide leaks!)
For knuckle rebuild:
Get a beer and watch this 3x
Best tutorial on knuckle rebuild I know.
If you do it: Do it once and complete.
Bearings, Oilseals, Gaskets, Brass-bearing or roller bearing upgrade. If needed: Brake rotor and front flex brakehoses.
Get a Workshop manual and study the procedures.
Get into the parts diagrams and understand, together with the video, how things fit together.
Get all the parts and you are golden for a long time.
No very special tools required. You need a proper puller to remove the steering joint (don't even try without) and a brass drift for the races, and a puller for the seals. That's it.
Mayhew Pro 25076 1/2 Zoll...
Amazon product ASIN B002XMSBBISilverline 282610...
https://www.amazon.de/dp/B000WTPJK0?ref=ppx_pop_mob_ap_share
Kugelgelenk Ausdrücker Werkzeug I 2-Fach Verstellbar bis 55mm I Maulöffnung: 20-22mm I Kugelenk-Abzieher
https://amzn.eu/d/61C80ta (check for correct size)
A brass or hard-plastic hammer.
All the rest is usual tools.
Drive out the old races, cut a slit in them and use them to drive in the new seals. (The slit allows them to easily come out again).
Takes you 5h on the first side and 3h on the other, once you know the procedure.
You can do it!
Good Luck Ralf.