To combine the two dataTags you need to move the tag
compound from first command into the inventory item compound in the second:
/testfor @p[r=10] {SelectedItemSlot:0,Inventory:[{Slot:0b,id:"minecraft:diamond_sword",tag:{display:{Name:"Item Name"}}}]}
Note: This will only test true if the item is in slot 0 and it is also the selected item.
You can use the SelectedItem tag instead of the SelectedItemSlot tag. This will allow you to target any player who currently has the specified item selected no matter which slot it is in:
/testfor @p[r=10] {SelectedItem:{id:"minecraft:diamond_sword",tag:{display:{Name:"Item Name"}}}}
As of 1.9 you can use scoreboard add tag command to tag the player holding the specific item.
scoreboard players tag @a add <tagName> {SelectedItem:{id:"minecraft:diamond_sword",tag:{display:{Name:"Item Name"}}}}
This allows you to target the players within another command. Lets make the players with the selected sword say hello:
/execute @a[tag=<tagName>] ~ ~ ~ say hello
You could use this tag in the item summon commands.
Then to remove the tag from all player:
scoreboard players tag @a remove <tagName>
If you want to test for any player holding any item with the correct name, simply omit the id portion of the dataTag:
/testfor @p[r=10] {SelectedItem:{tag:{display:{Name:"Item Name"}}}}